A Philosophical Explosion

 

Glass drops demonstration in slow motion
(Starts after the ad)

Previously, we started a tour through Europe that followed the introduction of an item called a "glass drop,"  "Prince Rupert's drop" or "Dutch tear." [1] Today we will explore the attempt of an enlightenment philosopher to explain the phenomenon. First, take a look at the dramatic video (above) of an actual glass drop exploding in slow motion.

In the late seventeenth century, the demonstration of glass drops was sweeping through the parlors of Europe. Consisting of nothing more than palm sized piece of glass with a bulbous nose and a tail that tapered to a point, this little item became a topic of fascination for intellectuals and experimenters alike. [2] Formed by simply letting a gob of glass drip into a bucket of cold water, the fat end could endure strong blows with a hammer, yet snap off the slender tail and the whole piece would erupt into a hail of glass dust and fragments.

Thomas Hobbes
by John Mitchel Wright,
(National Portrait Gallery)

Robert Hooke conducted a series of experiments, and observed the results carefully under a microscope. He arrived at conclusions that were largely correct even though the very nature of matter was still under debate. The molten glass on the surface of the drop cooled rapidly, as the still molten interior cooled more slowly, the drop shrunk, leaving the inside compressed. The result was a highly stressed surface that resisted the hammer. Snapping the tail caused a shock wave of cracks to propagate through the drop, releasing the tension, shattering the entire object into fragments no larger than a grain of sand.

Fig. of glass drop,
Thomas Hobbes, Problematica Physica, 1662 

Enlightenment philosopher Thomas Hobbes was less successful in his attempt to explain the phenomenon, yet not entirely off the mark. [3] Hobbes asks us to consider all matter as possessing "circular internal motion" even when the object as a whole is at rest. He reasoned the heat generated in a glass furnace increased this internal motion both in its "compass" or extent and in speed. When the drop was quenched, the glass that hit the water first has its internal motion changed:

Because the main drop A comes first to the water, it is therefore first quenched, and consequently the motion of the parts of that drop, which by the fire were made to be moved in a larger compass, is by the water made to shrink into lesser circles towards the other end B, but with the same or not much less swiftness.

He further reasons that this action causes the glass to form a structure like threads that run the length of the drop:

Seeing also this motion in every small part of the glass, is not only circular, but proceeds also all along the glass from A to B, the whole motion compounded will be such as the motion of spinning any soft matter into thread, and will dispose the whole body of the glass in threads, which in other hard bodies are called the grain.

Finally, he concludes that all these "threads" are bundled together tightly at the tail end of the drop. When the tail is snapped, 

By the breaking of the glass at C, [the threads] be all at once set at liberty; and then all at once being suddenly unbent, like so many brittle and overbent bows, their strings breaking, be shivered in pieces.

A somewhat tortured connection could be made between Hobbes' theory of internal motion and molecular kinetics, but it is a stretch. The truth of the matter is that his explanation of the glass drop demonstration is elegant and unfortunately, it is also wrong. How did Robert Hooke arrive at a correct conclusion while Hobbes and many others failed? It is a good question because it gets to heart of how successful science is done. Part of the answer lay in Hooke's careful experimentation and detailed observations; he tests his theories wherever he can, and extends his senses with instruments like the microscope. Hobbes develops a series of analogies, but he never devises experiments to test them. To be fair, both men end with conclusions that go beyond what could be observed or measured at the time, and in that realm either one of them could have stumbled. In the end, a correct theory can only be one that does not contradict what actually happens in nature.

In science, obsessive testing and measuring is certainly necessary to arrive at correct conclusions, however it is not sufficient. In other words, there is no guaranteed path to ensure a correct explanation. For this reason alone it is essential to understand that the universe does not follow the laws of physics, it is the other way around; the universe does what it does whether we have a rule for it or not. The 'laws' are our best guess at how nature operates; calling them by that name is a bit pretentious. However, when these laws have been tested repeatedly by our brightest minds, when we observe they are consistent with nature whether peering at the infinitesimal through a microscope or across the galaxy through a telescope, that is what makes science worthy of celebration. [4]

[1] Paul Engle, Conciatore Blog, 2 January 2017; http://www.conciatore.org/2017/01/hookes-tears.html

[2] Niccolò Angelo Tinassi , ed., Il Giornale de Letterati: per tutto l'anno 1672 (Rome : Nicolò Angelo Tinassi, 1672), p. 95.

[3] Thomas Hobbes, Problematica Physica, 1662 (translated in English in 1682 as Seven Philosophical Problems) pp. 36-39, 146-148.

[4] For an interesting rhyme about glass drops recited by Benjamin Franklin see Engle, "Benjamin Franklin and his Gathering of Glassmakers" in Bulletin of the National American Glass Club, Spring/Summer 2016.

Video Credit: Glass drops demonstration in slow motion. courtesy of the American Ceramics Society http://ceramics.org/ceramic-tech-today/video-glass-science-of-prince-ruperts-drop-captured-with-high-speed-cameras

* This is an updated version of a post that first appeared on Conciatore Blog, on 7 January 2015.

Hooke's Tears

 

Glass drops or tears coated in glue,

after detonation, (cross section is left)

from Robert Hooke's

Micrographia 1664, between p. 10, 11.

In 1661, an Italian reprint of Antonio Neri’s book of glassmaking recipes appeared. One year later, an English translation was published in London by physician Christopher Merrett. As an appendix, Merrett included an account of “glass drops” or tears as demonstrated to the Royal Society. These were molten gathers of glass that were allowed to drip into a bucket of cold water and cool. They formed a round, bulbous front end and a tail that trailed off to a thin filament. What made them so fascinating was that the bulbous end can easily endure strong blows with a hammer, but when the thin filament tail is snapped off, the whole piece explodes into a hail of tiny fragments “and in the dark, sparks [flash] at every break of their surface.” [1]

These glass drops became a novelty at royal courts throughout Europe, given a glass furnace they were easy to make, easy to demonstrate, and never failed to amaze observers who had not seen them before. They sparked animated discussion in the many scientific societies that had sprung up; what forces of nature were involved that a piece of glass could resist a hammer yet explode into dust at the loss of its slender tail? 

In the late seventeenth century a Roman publisher by the name of Tinassi [2] regularly issued compilation of noteworthy letters. In his journal’s edition for the year 1672, he published two letters by Geminiano Montanari, a mathematics professor at the university in Bologna, both on the subject of glass drops. In the introduction, he suggests that these curiosities were

Believed to be introduced in Sweden, Holland, then in England, France and Italy; In Paris in the year 1656, many experiments were made at the Academia which met at the home of Mr. Montmor. [3] Many have written of this, among others Monconys [4] in his "Journey to England,” [5] Thomas Hobbes in his Problematica Physica, [6][…] and Christopher Merrett, which in the Latin translation of L’Arte Vetraria of Antonio Neri, [7] is inserted the experiences of the Royal [Society] of England, [and] Mr. Robert Hooke [8] in his Micrographia. [9]

At a time when the concepts of atoms and molecules were still being debated, the glass drops became a nucleus around which a new science developed of mechanical tension and compression. A simple drip of glass caused sharp minds to puzzle and to take a closer look. 

In  Micrographia, Robert Hooke wrote about how he “ground away neer two thirds of the ball, yet would it not fly to pieces, but now and then some small rings of it would snap and fly off, not without a brisk noise and quick motion, leaving the Surface of the drop whence it flew very prettily branched or creased, which was easily discoverable by the Microscope. This drop, after I had thus ground it, without at all impairing the remnant that was not ground away, I caused to fly immediately all into sand upon the nipping off of the very tip of its slender end.”

Hooke continues to describe coating drops in fish glue (isinglass) which was tough enough to hold the piece together when the tail was snapped. “The drop gave a crack like the rest, and gave my hand a pretty brisk impulse: but yet the skin and leather was so strong as to keep the parts from flying out of their former posture and, the skin being transparent, I found that the drop retained exactly its former figure and polish, but was grown perfectly opacious and all over flaw’d, all those flaws lying in the manner of rings, from bottom or blunt end, to the very top or small point.” (See illustration above.)

He discovers that heating the glass drop and then allowing it to cool slowly neutralizes the explosive effect. Finally, he puts it all together: rapid cooling of the surface causes the interior to be compressed like a spring. Snipping the tail, where the skin is thinnest releases all the pent-up energy at once and the piece explodes.


[1] Tinassi 1672, p. 95.
[2] Niccolò Angelo Tinassi, active 1654-1690.
[3] Henri-Louis Habert de Montmor (c. 1600–1679), founded the Montmor Academy, which met at his house in Paris from 1657 until its dissolution in 1664.
[4] Balthasar de Monconys (1611–1665). 
[5] Monconys 1677,  for glass drops see pp. 32, 42 (fig. 4). https://books.google.com/books?id=L0b687oZRVQC
[6] 1662. Problematica Physica (translated in English in 1682 as Seven Philosophical Problems)
[7] This reference is not to Merrett’s 1662 translation of Neri (1612), but to the 1668 or 1669 edition by Frisius in Amsterdam which includes Merret’s annotations.
[8] Robert Hooke (1635–1703). 
[9] Hooke 1664, pp. 33–44.
*This post first appeared here 2 January 2015

Hooke's Tears

Glass drops or tears coated in glue,

after detonation, (cross section is left)

from Robert Hooke's

Micrographia 1664, between p. 10, 11.

In 1661, an Italian reprint of Antonio Neri’s book of glassmaking recipes appeared. One year later, an English translation was published in London by physician Christopher Merrett. As an appendix, Merrett included an account of “glass drops” or tears as demonstrated to the Royal Society. These were molten gathers of glass that were allowed to drip into a bucket of cold water and cool. They formed a round, bulbous front end and a tail that trailed off to a thin filament. What made them so fascinating was that the bulbous end can easily endure strong blows with a hammer, but when the thin filament tail is snapped off, the whole piece explodes into a hail of tiny fragments “and in the dark, sparks [flash] at every break of their surface.” [1]

These glass drops became a novelty at royal courts throughout Europe, given a glass furnace they were easy to make, easy to demonstrate, and never failed to amaze observers who had not seen them before. They sparked animated discussion in the many scientific societies that had sprung up; what forces of nature were involved that a piece of glass could resist a hammer yet explode into dust at the loss of its slender tail? 

In the late seventeenth century a Roman publisher by the name of Tinassi [2] regularly issued compilation of noteworthy letters. In his journal’s edition for the year 1672, he published two letters by Geminiano Montanari, a mathematics professor at the university in Bologna, both on the subject of glass drops. In the introduction, he suggests that these curiosities were

Believed to be introduced in Sweden, Holland, then in England, France and Italy; In Paris in the year 1656, many experiments were made at the Academia which met at the home of Mr. Montmor. [3] Many have written of this, among others Monconys [4] in his "Journey to England,” [5] Thomas Hobbes in his Problematica Physica, [6][…] and Christopher Merrett, which in the Latin translation of L’Arte Vetraria of Antonio Neri, [7] is inserted the experiences of the Royal [Society] of England, [and] Mr. Robert Hooke [8] in his Micrographia. [9]

At a time when the concepts of atoms and molecules were still being debated, the glass drops became a nucleus around which a new science developed of mechanical tension and compression. A simple drip of glass caused sharp minds to puzzle and to take a closer look. 

In  Micrographia, Robert Hooke wrote about how he “ground away neer two thirds of the ball, yet would it not fly to pieces, but now and then some small rings of it would snap and fly off, not without a brisk noise and quick motion, leaving the Surface of the drop whence it flew very prettily branched or creased, which was easily discoverable by the Microscope. This drop, after I had thus ground it, without at all impairing the remnant that was not ground away, I caused to fly immediately all into sand upon the nipping off of the very tip of its slender end.”

Hooke continues to describe coating drops in fish glue (isinglass) which was tough enough to hold the piece together when the tail was snapped. “The drop gave a crack like the rest, and gave my hand a pretty brisk impulse: but yet the skin and leather was so strong as to keep the parts from flying out of their former posture and, the skin being transparent, I found that the drop retained exactly its former figure and polish, but was grown perfectly opacious and all over flaw’d, all those flaws lying in the manner of rings, from bottom or blunt end, to the very top or small point.” (See illustration above.)

He discovers that heating the glass drop and then allowing it to cool slowly neutralizes the explosive effect. Finally, he puts it all together: rapid cooling of the surface causes the interior to be compressed like a spring. Snipping the tail, where the skin is thinnest releases all the pent-up energy at once and the piece explodes.


[1] Tinassi 1672, p. 95.
[2] Niccolò Angelo Tinassi, active 1654-1690.
[3] Henri-Louis Habert de Montmor (c. 1600–1679), founded the Montmor Academy, which met at his house in Paris from 1657 until its dissolution in 1664.
[4] Balthasar de Monconys (1611–1665). 
[5] Monconys 1677,  for glass drops see pp. 32, 42 (fig. 4). https://books.google.com/books?id=L0b687oZRVQC
[6] 1662. Problematica Physica (translated in English in 1682 as Seven Philosophical Problems)
[7] This reference is not to Merrett’s 1662 translation of Neri (1612), but to the 1668 or 1669 edition by Frisius in Amsterdam which includes Merret’s annotations.
[8] Robert Hooke (1635–1703). 
[9] Hooke 1664, pp. 33–44.
*This post first appeared here 2 January 2015

Hooke's Tears

Glass drops or tears coated in glue,

after detonation, (cross section is left)

from Robert Hooke's

Micrographia 1664, between p. 10, 11.

In 1661, an Italian reprint of Antonio Neri’s book of glassmaking recipes appeared. One year later, an English translation was published in London by physician Christopher Merrett. As an appendix, Merrett included an account of “glass drops” or tears as demonstrated to the Royal Society. These were molten gathers of glass that were allowed to drip into a bucket of cold water and cool. They formed a round, bulbous front end and a tail that trailed off to a thin filament. What made them so fascinating was that the bulbous end can easily endure strong blows with a hammer, but when the thin filament tail is snapped off, the whole piece explodes into a hail of tiny fragments “and in the dark, sparks [flash] at every break of their surface.” [1]

These glass drops became a novelty at royal courts throughout Europe, given a glass furnace they were easy to make, easy to demonstrate, and never failed to amaze observers who had not seen them before. They sparked animated discussion in the many scientific societies that had sprung up; what forces of nature were involved that a piece of glass could resist a hammer yet explode into dust at the loss of its slender tail? 

In the late seventeenth century a Roman publisher by the name of Tinassi [2] regularly issued compilation of noteworthy letters. In his journal’s edition for the year 1672, he published two letters by Geminiano Montanari, a mathematics professor at the university in Bologna, both on the subject of glass drops. In the introduction, he suggests that these curiosities were

Believed to be introduced in Sweden, Holland, then in England, France and Italy; In Paris in the year 1656, many experiments were made at the Academia which met at the home of Mr. Montmor. [3] Many have written of this, among others Monconys [4] in his "Journey to England,” [5] Thomas Hobbes in his Problematica Physica, [6][…] and Christopher Merrett, which in the Latin translation of L’Arte Vetraria of Antonio Neri, [7] is inserted the experiences of the Royal [Society] of England, [and] Mr. Robert Hooke [8] in his Micrographia. [9]

At a time when the concepts of atoms and molecules were still being debated, the glass drops became a nucleus around which a new science developed of mechanical tension and compression. A simple drip of glass caused sharp minds to puzzle and to take a closer look. 

In  Micrographia, Robert Hooke wrote about how he “ground away neer two thirds of the ball, yet would it not fly to pieces, but now and then some small rings of it would snap and fly off, not without a brisk noise and quick motion, leaving the Surface of the drop whence it flew very prettily branched or creased, which was easily discoverable by the Microscope. This drop, after I had thus ground it, without at all impairing the remnant that was not ground away, I caused to fly immediately all into sand upon the nipping off of the very tip of its slender end.”

Hooke continues to describe coating drops in fish glue (isinglass) which was tough enough to hold the piece together when the tail was snapped. “The drop gave a crack like the rest, and gave my hand a pretty brisk impulse: but yet the skin and leather was so strong as to keep the parts from flying out of their former posture and, the skin being transparent, I found that the drop retained exactly its former figure and polish, but was grown perfectly opacious and all over flaw’d, all those flaws lying in the manner of rings, from bottom or blunt end, to the very top or small point.” (See illustration above.)

He discovers that heating the glass drop and then allowing it to cool slowly neutralizes the explosive effect. Finally, he puts it all together: rapid cooling of the surface causes the interior to be compressed like a spring. Snipping the tail, where the skin is thinnest releases all the pent-up energy at once and the piece explodes.


[1] Tinassi 1672, p. 95.
[2] Niccolò Angelo Tinassi, active 1654-1690.
[3] Henri-Louis Habert de Montmor (c. 1600–1679), founded the Montmor Academy, which met at his house in Paris from 1657 until its dissolution in 1664.
[4] Balthasar de Monconys (1611–1665). 
[5] Monconys 1677,  for glass drops see pp. 32, 42 (fig. 4). https://books.google.com/books?id=L0b687oZRVQC
[6] 1662. Problematica Physica (translated in English in 1682 as Seven Philosophical Problems)
[7] This reference is not to Merrett’s 1662 translation of Neri (1612), but to the 1668 or 1669 edition by Frisius in Amsterdam which includes Merret’s annotations.
[8] Robert Hooke (1635–1703). 
[9] Hooke 1664, pp. 33–44.
*This post first appeared here 2 January 2015

Philosophical Explosion

Glass drops demonstration in slow motion
(Starts after the ad)

Previously, we started a tour through Europe that followed the introduction of an item called a "glass drop,"  "Prince Rupert's drop" or "Dutch tear." [1] Today we will explore the attempt of an enlightenment philosopher to explain the phenomenon. First, take a look at the dramatic video (above) of an actual glass drop exploding in slow motion.

In the late seventeenth century, the demonstration of glass drops was sweeping through the parlors of Europe. Consisting of nothing more than palm sized piece of glass with a bulbous nose and a tail that tapered to a point, this little item became a topic of fascination for intellectuals and experimenters alike. [2] Formed by simply letting a gob of glass drip into a bucket of cold water, the fat end could endure strong blows with a hammer, yet snap off the slender tail and the whole piece would erupt into a hail of glass dust and fragments.

Thomas Hobbes
by John Mitchel Wright,
(National Portrait Gallery)

Robert Hooke conducted a series of experiments, and observed the results carefully under a microscope. He arrived at conclusions that were largely correct even though the very nature of matter was still under debate. The molten glass on the surface of the drop cooled rapidly, as the still molten interior cooled more slowly, the drop shrunk, leaving the inside compressed. The result was a highly stressed surface that resisted the hammer. Snapping the tail caused a shock wave of cracks to propagate through the drop, releasing the tension, shattering the entire object into fragments no larger than a grain of sand.

Fig. of glass drop,
Thomas Hobbes, Problematica Physica, 1662 

Enlightenment philosopher Thomas Hobbes was less successful in his attempt to explain the phenomenon, yet not entirely off the mark. [3] Hobbes asks us to consider all matter as possessing "circular internal motion" even when the object as a whole is at rest. He reasoned the heat generated in a glass furnace increased this internal motion both in its "compass" or extent and in speed. When the drop was quenched, the glass that hit the water first has its internal motion changed:

Because the main drop A comes first to the water, it is therefore first quenched, and consequently the motion of the parts of that drop, which by the fire were made to be moved in a larger compass, is by the water made to shrink into lesser circles towards the other end B, but with the same or not much less swiftness.

He further reasons that this action causes the glass to form a structure like threads that run the length of the drop:

Seeing also this motion in every small part of the glass, is not only circular, but proceeds also all along the glass from A to B, the whole motion compounded will be such as the motion of spinning any soft matter into thread, and will dispose the whole body of the glass in threads, which in other hard bodies are called the grain.

Finally, he concludes that all these "threads" are bundled together tightly at the tail end of the drop. When the tail is snapped, 

By the breaking of the glass at C, [the threads] be all at once set at liberty; and then all at once being suddenly unbent, like so many brittle and overbent bows, their strings breaking, be shivered in pieces.

A somewhat tortured connection could be made between Hobbes' theory of internal motion and molecular kinetics, but it is a stretch. The truth of the matter is that his explanation of the glass drop demonstration is elegant and unfortunately, it is also wrong. How did Robert Hooke arrive at a correct conclusion while Hobbes and many others failed? It is a good question because it gets to heart of how successful science is done. Part of the answer lay in Hooke's careful experimentation and detailed observations; he tests his theories wherever he can, and extends his senses with instruments like the microscope. Hobbes develops a series of analogies, but he never devises experiments to test them. To be fair, both men end with conclusions that go beyond what could be observed or measured at the time, and in that realm either one of them could have stumbled. In the end, a correct theory can only be one that does not contradict what actually happens in nature.

In science, obsessive testing and measuring is certainly necessary to arrive at correct conclusions, however it is not sufficient. In other words, there is no guaranteed path to ensure a correct explanation. For this reason alone it is essential to understand that the universe does not follow the laws of physics, it is the other way around; the universe does what it does whether we have a rule for it or not. The 'laws' are our best guess at how nature operates; calling them by that name is a bit pretentious. However, when these laws have been tested repeatedly by our brightest minds, when we observe they are consistent with nature whether peering at the infinitesimal through a microscope or across the galaxy through a telescope, that is what makes science worthy of celebration. [4]

[1] Paul Engle, Conciatore Blog, 2 January 2017; http://www.conciatore.org/2017/01/hookes-tears.html

[2] Niccolò Angelo Tinassi , ed., Il Giornale de Letterati: per tutto l'anno 1672 (Rome : Nicolò Angelo Tinassi, 1672), p. 95.

[3] Thomas Hobbes, Problematica Physica, 1662 (translated in English in 1682 as Seven Philosophical Problems) pp. 36-39, 146-148.

[4] For an interesting rhyme about glass drops recited by Benjamin Franklin see Engle, "Benjamin Franklin and his Gathering of Glassmakers" in Bulletin of the National American Glass Club, Spring/Summer 2016.

Video Credit: Glass drops demonstration in slow motion. courtesy of the American Ceramics Society http://ceramics.org/ceramic-tech-today/video-glass-science-of-prince-ruperts-drop-captured-with-high-speed-cameras

* This is an updated version of a post that first appeared on Conciatore Blog, on 7 January 2015.

Hooke's Tears

Glass drops or tears coated in glue,

after detonation, (cross section is left)

from Robert Hooke's

Micrographia 1664, between p. 10, 11.

In 1661, an Italian reprint of Antonio Neri’s book of glassmaking recipes appeared. One year later, an English translation was published in London by physician Christopher Merrett. As an appendix, Merrett included an account of “glass drops” or tears as demonstrated to the Royal Society. These were molten gathers of glass that were allowed to drip into a bucket of cold water and cool. They formed a round, bulbous front end and a tail that trailed off to a thin filament. What made them so fascinating was that the bulbous end can easily endure strong blows with a hammer, but when the thin filament tail is snapped off, the whole piece explodes into a hail of tiny fragments “and in the dark, sparks [flash] at every break of their surface.” [1]

These glass drops became a novelty at royal courts throughout Europe, given a glass furnace they were easy to make, easy to demonstrate, and never failed to amaze observers who had not seen them before. They sparked animated discussion in the many scientific societies that had sprung up; what forces of nature were involved that a piece of glass could resist a hammer yet explode into dust at the loss of its slender tail? 

In the late seventeenth century a Roman publisher by the name of Tinassi [2] regularly issued compilation of noteworthy letters. In his journal’s edition for the year 1672, he published two letters by Geminiano Montanari, a mathematics professor at the university in Bologna, both on the subject of glass drops. In the introduction, he suggests that these curiosities were

Believed to be introduced in Sweden, Holland, then in England, France and Italy; In Paris in the year 1656, many experiments were made at the Academia which met at the home of Mr. Montmor. [3] Many have written of this, among others Monconys [4] in his "Journey to England,” [5] Thomas Hobbes in his Problematica Physica, [6][…] and Christopher Merrett, which in the Latin translation of L’Arte Vetraria of Antonio Neri, [7] is inserted the experiences of the Royal [Society] of England, [and] Mr. Robert Hooke [8] in his Micrographia. [9]

At a time when the concepts of atoms and molecules were still being debated, the glass drops became a nucleus around which a new science developed of mechanical tension and compression. A simple drip of glass caused sharp minds to puzzle and to take a closer look. 

In  Micrographia, Robert Hooke wrote about how he “ground away neer two thirds of the ball, yet would it not fly to pieces, but now and then some small rings of it would snap and fly off, not without a brisk noise and quick motion, leaving the Surface of the drop whence it flew very prettily branched or creased, which was easily discoverable by the Microscope. This drop, after I had thus ground it, without at all impairing the remnant that was not ground away, I caused to fly immediately all into sand upon the nipping off of the very tip of its slender end.”

Hooke continues to describe coating drops in fish glue (isinglass) which was tough enough to hold the piece together when the tail was snapped. “The drop gave a crack like the rest, and gave my hand a pretty brisk impulse: but yet the skin and leather was so strong as to keep the parts from flying out of their former posture and, the skin being transparent, I found that the drop retained exactly its former figure and polish, but was grown perfectly opacious and all over flaw’d, all those flaws lying in the manner of rings, from bottom or blunt end, to the very top or small point.” (See illustration above.)

He discovers that heating the glass drop and then allowing it to cool slowly neutralizes the explosive effect. Finally, he puts it all together: rapid cooling of the surface causes the interior to be compressed like a spring. Snipping the tail, where the skin is thinnest releases all the pent-up energy at once and the piece explodes.


[1] Tinassi 1672, p. 95.
[2] Niccolò Angelo Tinassi, active 1654-1690.
[3] Henri-Louis Habert de Montmor (c. 1600–1679), founded the Montmor Academy, which met at his house in Paris from 1657 until its dissolution in 1664.
[4] Balthasar de Monconys (1611–1665). 
[5] Monconys 1677,  for glass drops see pp. 32, 42 (fig. 4). https://books.google.com/books?id=L0b687oZRVQC
[6] 1662. Problematica Physica (translated in English in 1682 as Seven Philosophical Problems)
[7] This reference is not to Merrett’s 1662 translation of Neri (1612), but to the 1668 or 1669 edition by Frisius in Amsterdam which includes Merret’s annotations.
[8] Robert Hooke (1635–1703). 
[9] Hooke 1664, pp. 33–44.
*This post first appeared here 2 January 2015

A Philosophical Explosion

Glass drops demonstration in slow motion

Previously, we started a tour through Europe that followed the introduction of an item called a "glass drop,"  "Prince Rupert's drop" or "Dutch tear." [1] Today we will explore the attempt of an enlightenment philosopher to explain the phenomenon. First, take a look at the dramatic video (above) of an actual glass drop exploding in slow motion.

In the late seventeenth century, the demonstration of glass drops was sweeping through the parlors of Europe. Consisting of nothing more than palm sized piece of glass with a bulbous nose and a tail that tapered to a point, this little item became a topic of fascination for intellectuals and experimenters alike. [2] Formed by simply letting a gob of glass drip into a bucket of cold water, the fat end could endure strong blows with a hammer, yet snap off the slender tail and the whole piece would erupt into a hail of glass dust and fragments.

Thomas Hobbes
by John Mitchel Wright,
(National Portrait Gallery)

Robert Hooke conducted a series of experiments, and observed the results carefully under a microscope. He arrived at conclusions that were largely correct even though the very nature of matter was still under debate. The molten glass on the surface of the drop cooled rapidly, shrunk, and compressed the interior. The result was a highly stressed surface that resisted the hammer. Snapping the tail caused a shock wave of cracks to propagate through the drop, releasing the tension, shattering the entire object into fragments no larger than a grain of sand.

Fig. of glass drop,
Thomas Hobbes, Problematica Physica, 1662 

Enlightenment philosopher Thomas Hobbes was less successful in his attempt to explain the phenomenon, yet not entirely off the mark. [3] Hobbes asks us to consider all matter as possessing "circular internal motion" even when the object as a whole is at rest. He reasoned the heat generated in a glass furnace increased this internal motion both in its "compass" or extent and in speed. When the drop was quenched, the glass that hit the water first has its internal motion changed:

Because the main drop A comes first to the water, it is therefore first quenched, and consequently the motion of the parts of that drop, which by the fire were made to be moved in a larger compass, is by the water made to shrink into lesser circles towards the other end B, but with the same or not much less swiftness.

He further reasons that this action causes the glass to form a structure like threads that run the length of the drop:

Seeing also this motion in every small part of the glass, is not only circular, but proceeds also all along the glass from A to B, the whole motion compounded will be such as the motion of spinning any soft matter into thread, and will dispose the whole body of the glass in threads, which in other hard bodies are called the grain.

Finally, he concludes that all these "threads" are bundled together tightly at the tail end of the drop. When the tail is snapped, 

By the breaking of the glass at C, [the threads] be all at once set at liberty; and then all at once being suddenly unbent, like so many brittle and overbent bows, their strings breaking, be shivered in pieces.

A somewhat tortured connection could be made between Hobbes' theory of internal motion and molecular kinetics, but it is a stretch. The truth of the matter is that his explanation of the glass drop demonstration is elegant and unfortunately, it is also wrong. How did Robert Hooke arrive at a correct conclusion while Hobbes and many others failed? It is a good question because it gets to heart of how successful science is done. Part of the answer lay in Hooke's careful experimentation and detailed observations; he tests his theories wherever he can, and extends his senses with instruments like the microscope. Hobbes develops a series of analogies, but he never devises experiments to test them. To be fair, both men end with conclusions that go beyond what could be observed or measured at the time, and in that realm either one of them could have stumbled. In the end, a correct theory can only be one that does not contradict what actually happens in nature.

In science, obsessive testing and measuring is certainly necessary to arrive at correct conclusions, however it is not sufficient. In other words, there is no guaranteed path to ensure a correct explanation. For this reason alone it is essential to understand that the universe does not follow the laws of physics, it is the other way around; the universe does what it does whether we have a rule for it or not. The 'laws' are our best guess at how nature operates; calling them by that name is a bit pretentious. However, when these laws have been tested repeatedly by our brightest minds, when we observe they are consistent with nature whether peering at the infinitesimal through a microscope or across the galaxy through a telescope, that is what makes science worthy of celebration. [4]

[1] Paul Engle, Conciatore Blog, 2 January 2017; http://www.conciatore.org/2017/01/hookes-tears.html

[2] Niccolò Angelo Tinassi , ed., Il Giornale de Letterati: per tutto l'anno 1672 (Rome : Nicolò Angelo Tinassi, 1672), p. 95.

[3] Thomas Hobbes, Problematica Physica, 1662 (translated in English in 1682 as Seven Philosophical Problems) pp. 36-39, 146-148.

[4] For an interesting rhyme about glass drops recited by Benjamin Franklin see Engle, "Benjamin Franklin and his Gathering of Glassmakers" in Bulletin of the National American Glass Club, Spring/Summer 2016.

Video Credit: Glass drops demonstration in slow motion. courtesy of the American Ceramics Society http://ceramics.org/ceramic-tech-today/video-glass-science-of-prince-ruperts-drop-captured-with-high-speed-cameras

* This is an updated version of a post that first appeared on Conciatore Blog, on 7 January 2015.

Hooke's Tears

Glass drops or tears coated in glue,

after detonation, (cross section is left)

from Robert Hooke's

Micrographia 1664, between p. 10, 11.

In 1661, an Italian reprint of Antonio Neri’s book of glassmaking recipes appeared. One year later, an English translation was published in London by physician Christopher Merrett. As an appendix, Merrett included an account of “glass drops” or tears as demonstrated to the Royal Society. These were molten gathers of glass that were allowed to drip into a bucket of cold water and cool. They formed a round, bulbous front end and a tail that trailed off to a thin filament. What made them so fascinating was that the bulbous end can easily endure strong blows with a hammer, but when the thin filament tail is snapped off, the whole piece explodes into a hail of tiny fragments “and in the dark, sparks [flash] at every break of their surface.” [1]

These glass drops became a novelty at royal courts throughout Europe, given a glass furnace they were easy to make, easy to demonstrate, and never failed to amaze observers who had not seen them before. They sparked animated discussion in the many scientific societies that had sprung up; what forces of nature were involved that a piece of glass could resist a hammer yet explode into dust at the loss of its slender tail? 

In the late seventeenth century a Roman publisher by the name of Tinassi [2] regularly issued compilation of noteworthy letters. In his journal’s edition for the year 1672, he published two letters by Geminiano Montanari, a mathematics professor at the university in Bologna, both on the subject of glass drops. In the introduction, he suggests that these curiosities were

Believed to be introduced in Sweden, Holland, then in England, France and Italy; In Paris in the year 1656, many experiments were made at the Academia which met at the home of Mr. Montmor. [3] Many have written of this, among others Monconys [4] in his "Journey to England,” [5] Thomas Hobbes in his Problematica Physica, [6][…] and Christopher Merrett, which in the Latin translation of L’Arte Vetraria of Antonio Neri, [7] is inserted the experiences of the Royal [Society] of England, [and] Mr. Robert Hooke [8] in his Micrographia. [9]

At a time when the concepts of atoms and molecules were still being debated, the glass drops became a nucleus around which a new science developed of mechanical tension and compression. A simple drip of glass caused sharp minds to puzzle and to take a closer look. 

In  Micrographia, Robert Hooke wrote about how he “ground away neer two thirds of the ball, yet would it not fly to pieces, but now and then some small rings of it would snap and fly off, not without a brisk noise and quick motion, leaving the Surface of the drop whence it flew very prettily branched or creased, which was easily discoverable by the Microscope. This drop, after I had thus ground it, without at all impairing the remnant that was not ground away, I caused to fly immediately all into sand upon the nipping off of the very tip of its slender end.”

Hooke continues to describe coating drops in fish glue (isinglass) which was tough enough to hold the piece together when the tail was snapped. “The drop gave a crack like the rest, and gave my hand a pretty brisk impulse: but yet the skin and leather was so strong as to keep the parts from flying out of their former posture and, the skin being transparent, I found that the drop retained exactly its former figure and polish, but was grown perfectly opacious and all over flaw’d, all those flaws lying in the manner of rings, from bottom or blunt end, to the very top or small point.” (See illustration above.)

He discovers that heating the glass drop and then allowing it to cool slowly neutralizes the explosive effect. Finally, he puts it all together: rapid cooling of the surface causes the interior to be compressed like a spring. Snipping the tail, where the skin is thinnest releases all the pent-up energy at once and the piece explodes.


[1] Tinassi 1672, p. 95.
[2] Niccolò Angelo Tinassi, active 1654-1690.
[3] Henri-Louis Habert de Montmor (c. 1600–1679), founded the Montmor Academy, which met at his house in Paris from 1657 until its dissolution in 1664.
[4] Balthasar de Monconys (1611–1665). 
[5] Monconys 1677,  for glass drops see pp. 32, 42 (fig. 4). https://books.google.com/books?id=L0b687oZRVQC
[6] 1662. Problematica Physica (translated in English in 1682 as Seven Philosophical Problems)
[7] This reference is not to Merrett’s 1662 translation of Neri (1612), but to the 1668 or 1669 edition by Frisius in Amsterdam which includes Merret’s annotations.
[8] Robert Hooke (1635–1703). 
[9] Hooke 1664, pp. 33–44.

*This post first appeared here 2 January 2015

Thomas Hobbes on Glass

Thomas Hobbes

by John Michael Wright , (National Portrait Gallery).

Last week we started a tour through Europe that followed the introduction of an item called a "glass drop,"  "Prince Rupert's drop" or "Dutch tear." [1] Today we will explore the attempt of an enlightenment philosopher to explain the phenomenon. First, here is a brief refresher.

In the late seventeenth century, the demonstration of glass drops was sweeping through the parlors of Europe. Consisting of nothing more than palm sized piece of glass with a bulbous nose and a tail that tapered to a point, this little item became a topic of fascination for intellectuals and experimenters alike. [2] Formed by simply letting a gob of glass drip into a bucket of cold water, the fat end could endure strong blows with a hammer, yet snap off the slender tail and the whole piece would erupt into a hail of glass dust and fragments.

Robert Hooke conducted a series of experiments, and observed the results carefully under a microscope. He arrived at conclusions that were largely correct even though the very nature of matter was still under debate. The molten glass on the surface of the drop cooled rapidly, shrunk, and compressed the interior. The result was a highly stressed surface that resisted the hammer. Snapping the tail caused a shock wave of cracks to propagate through the drop, releasing the tension, shattering the entire object into fragments no larger than a grain of sand.

Fig. of glass drop,
Thomas Hobbes, Problematica Physica, 1662 

Enlightenment philosopher Thomas Hobbes was less successful in his attempt to explain the phenomenon, yet not entirely off the mark. [3] Hobbes asks us to consider all matter as possessing "circular internal motion" even when the object as a whole is at rest. He reasoned the heat generated in a glass furnace increased this internal motion both in its "compass" or extent and in speed. When the drop was quenched, the glass that hit the water first has its internal motion changed:

Because the main drop A comes first to the water, it is therefore first quenched, and consequently the motion of the parts of that drop, which by the fire were made to be moved in a larger compass, is by the water made to shrink into lesser circles towards the other end B, but with the same or not much less swiftness.

He further reasons that this action causes the glass to form a structure like threads that run the length of the drop:

Seeing also this motion in every small part of the glass, is not only circular, but proceeds also all along the glass from A to B, the whole motion compounded will be such as the motion of spinning any soft matter into thread, and will dispose the whole body of the glass in threads, which in other hard bodies are called the grain.

Finally, he concludes that all these "threads" are bundled together tightly at the tail end of the drop. When the tail is snapped, 

By the breaking of the glass at C, [the threads] be all at once set at liberty; and then all at once being suddenly unbent, like so many brittle and overbent bows, their strings breaking, be shivered in pieces.

A somewhat tortured connection could be made between Hobbes' theory of internal motion and molecular kinetics, but it is a stretch. The truth of the matter is that his explanation of the glass drop demonstration is elegant and unfortunately, it is also wrong. How did Robert Hooke arrive at a correct conclusion while Hobbes and many others failed? It is a good question because it gets to heart of how successful science is done. Part of the answer lay in Hooke's careful experimentation and detailed observations; he tests his theories wherever he can, and extends his senses with instruments like the microscope. Hobbes develops a series of analogies, but he never devises experiments to test them. To be fair, both men end with conclusions that go beyond what could be observed or measured at the time, and in that realm either one of them could have stumbled. In the end, a correct theory can only be one that does not contradict what actually happens in nature.

In science, obsessive testing and measuring is certainly necessary to arrive at correct conclusions, however it is not sufficient. In other words, there is no guaranteed path to ensure a correct explanation. For this reason alone it is essential to understand that the universe does not follow the laws of physics, it is the other way around; the universe does what it does whether we have a rule for it or not. The 'laws' are our best guess at how nature operates; calling them by that name is a bit pretentious. However, when these laws have been tested repeatedly by our brightest minds, when we observe they are consistent with nature whether peering at the infinitesimal through a microscope or across the galaxy through a telescope, that is what makes science worthy of celebration. [4]

[1] Paul Engle, Conciatore Blog, 2 January 2017; http://www.conciatore.org/2017/01/hookes-tears.html
[2] Niccolò Angelo Tinassi , ed., Il Giornale de Letterati: per tutto l'anno 1672 (Rome : Nicolò Angelo Tinassi, 1672), p. 95.
[3] Thomas Hobbes, Problematica Physica, 1662 (translated in English in 1682 as Seven Philosophical Problems) pp. 36-39, 146-148.
[4] For an interesting rhyme about glass drops recited by Benjamin Franklin see Engle, "Benjamin Franklin and his Gathering of Glassmakers" in Bulletin of the National American Glass Club, Spring/Summer 2016.
* This is an updated version of a post that first appeared on Conciatore Blog, on 7 January 2015.

Hooke's Tears

Glass drops or tears coated in glue,

after detonation, (cross section is left)

from Robert Hooke's

Micrographia 1664, between p. 10, 11.

In 1661, an Italian reprint of Antonio Neri’s book of glassmaking recipes appeared. One year later, an English translation was published in London by physician Christopher Merrett. As an appendix, Merrett included an account of “glass drops” or tears as demonstrated to the Royal Society. These were molten gathers of glass that were allowed to drip into a bucket of cold water and cool. They formed a round, bulbous front end and a tail that trailed off to a thin filament. What made them so fascinating was that the bulbous end can easily endure strong blows with a hammer, but when the thin filament tail is snapped off, the whole piece explodes into a hail of tiny fragments “and in the dark, sparks [flash] at every break of their surface.” [1]

These glass drops became a novelty at royal courts throughout Europe, given a glass furnace they were easy to make, easy to demonstrate, and never failed to amaze observers who had not seen them before. They sparked animated discussion in the many scientific societies that had sprung up; what forces of nature were involved that a piece of glass could resist a hammer yet explode into dust at the loss of its slender tail? 

In the late seventeenth century a Roman publisher by the name of Tinassi [2] regularly issued compilation of noteworthy letters. In his journal’s edition for the year 1672, he published two letters by Geminiano Montanari, a mathematics professor at the university in Bologna, both on the subject of glass drops. In the introduction, he suggests that these curiosities were

Believed to be introduced in Sweden, Holland, then in England, France and Italy; In Paris in the year 1656, many experiments were made at the Academia which met at the home of Mr. Montmor. [3] Many have written of this, among others Monconys [4] in his "Journey to England,” [5] Thomas Hobbes in his Problematica Physica, [6][…] and Christopher Merrett, which in the Latin translation of L’Arte Vetraria of Antonio Neri, [7] is inserted the experiences of the Royal [Society] of England, [and] Mr. Robert Hooke [8] in his Micrographia. [9]

At a time when the concepts of atoms and molecules were still being debated, the glass drops became a nucleus around which a new science developed of mechanical tension and compression. A simple drip of glass caused sharp minds to puzzle and to take a closer look. 

In  Micrographia, Robert Hooke wrote about how he “ground away neer two thirds of the ball, yet would it not fly to pieces, but now and then some small rings of it would snap and fly off, not without a brisk noise and quick motion, leaving the Surface of the drop whence it flew very prettily branched or creased, which was easily discoverable by the Microscope. This drop, after I had thus ground it, without at all impairing the remnant that was not ground away, I caused to fly immediately all into sand upon the nipping off of the very tip of its slender end.”

Hooke continues to describe coating drops in fish glue (isinglass) which was tough enough to hold the piece together when the tail was snapped. “The drop gave a crack like the rest, and gave my hand a pretty brisk impulse: but yet the skin and leather was so strong as to keep the parts from flying out of their former posture and, the skin being transparent, I found that the drop retained exactly its former figure and polish, but was grown perfectly opacious and all over flaw’d, all those flaws lying in the manner of rings, from bottom or blunt end, to the very top or small point.” (See illustration above.)

He discovers that heating the glass drop and then allowing it to cool slowly neutralizes the explosive effect. Finally, he puts it all together: rapid cooling of the surface causes the interior to be compressed like a spring. Snipping the tail, where the skin is thinnest releases all the pent-up energy at once and the piece explodes.


[1] Tinassi 1672, p. 95.
[2] Niccolò Angelo Tinassi, active 1654-1690.
[3] Henri-Louis Habert de Montmor (c. 1600–1679), founded the Montmor Academy, which met at his house in Paris from 1657 until its dissolution in 1664.
[4] Balthasar de Monconys (1611–1665). 
[5] Monconys 1677,  for glass drops see pp. 32, 42 (fig. 4). https://books.google.com/books?id=L0b687oZRVQC
[6] 1662. Problematica Physica (translated in English in 1682 as Seven Philosophical Problems)
[7] This reference is not to Merrett’s 1662 translation of Neri (1612), but to the 1668 or 1669 edition by Frisius in Amsterdam which includes Merret’s annotations.
[8] Robert Hooke (1635–1703). 
[9] Hooke 1664, pp. 33–44.

*This post first appeared here 2 January 2015

Thomas Hobbes on Glass

Thomas Hobbes

by John Michael Wright , (National Portrait Gallery).

Last week we started a tour through Europe that followed the introduction of an item called a "glass drop,"  "Prince Rupert's drop" or "Dutch tear." Today we will explore the attempt of an enlightenment philosopher to explain the phenomenon. First, here is a brief refresher.

In the late seventeenth century, the demonstration of glass drops was sweeping through the parlors of Europe. Consisting of nothing more than palm sized piece of glass with a bulbous nose and a tail that tapered to a point, this little item became a topic of fascination for intellectuals and experimenters alike. Formed by simply letting a gob of glass drip into a bucket of cold water, the fat end could endure strong blows with a hammer, yet snap off the slender tail and the whole piece would erupt into a hail of glass dust and fragments.

Robert Hooke conducted a series of experiments, and observed the results carefully under a microscope. He arrived at conclusions that were largely correct even though the very nature of matter was still under debate. The molten glass on the surface of the drop cooled rapidly, shrunk, and compressed the interior. The result was a highly stressed surface that resisted the hammer. Snapping the tail caused a shock wave of cracks to propagate through the drop, releasing the tension, shattering the entire object into fragments no larger than a grain of sand.

Fig. of glass drop,
Thomas Hobbes, Problematica Physica, 1662 

Enlightenment philosopher Thomas Hobbes was less successful in his attempt to explain the phenomenon, yet not entirely off the mark. [1] Hobbes asks us to consider all matter as possessing "circular internal motion" even when the object as a whole is at rest. He reasoned the heat generated in a glass furnace increased this internal motion both in its "compass" or extent and in speed. When the drop was quenched, the glass that hit the water first has its internal motion changed:

Because the main drop A comes first to the water, it is therefore first quenched, and consequently the motion of the parts of that drop, which by the fire were made to be moved in a larger compass, is by the water made to shrink into lesser circles towards the other end B, but with the same or not much less swiftness.

He further reasons that this action causes the glass to form a structure like threads that run the length of the drop:

Seeing also this motion in every small part of the glass, is not only circular, but proceeds also all along the glass from A to B, the whole motion compounded will be such as the motion of spinning any soft matter into thread, and will dispose the whole body of the glass in threads, which in other hard bodies are called the grain.

Finally, he concludes that all these "threads" are bundled together tightly at the tail end of the drop. When the tail is snapped, 

By the breaking of the glass at C, [the threads] be all at once set at liberty; and then all at once being suddenly unbent, like so many brittle and overbent bows, their strings breaking, be shivered in pieces.

A somewhat tortured connection could be made between Hobbes' theory of internal motion and molecular kinetics, but it is a stretch. The truth of the matter is that his explanation of the glass drop demonstration is elegant and unfortunately, it is also wrong. How did Robert Hooke arrive at a correct conclusion while Hobbes and many others failed? It is a good question because it gets to heart of how successful science is done. Part of the answer lay in Hooke's careful experimentation and detailed observations; he tests his theories wherever he can, and extends his senses with instruments like the microscope. Hobbes develops a series of analogies, but he never devises experiments to test them. To be fair, both men end with conclusions that go beyond what could be observed or measured at the time, and in that realm either one of them could have stumbled. In the end, a correct theory can only be one that does not contradict what actually happens in nature.

In science, obsessive testing and measuring is certainly necessary to arrive at correct conclusions, however it is not sufficient. In other words, there is no guaranteed path to ensure a correct explanation. For this reason alone it is essential to understand that the universe does not follow the laws of physics, it is the other way around; the universe does what it does whether we have a rule for it or not. The 'laws' are our best guess at how nature operates; calling them by that name is a bit pretentious. However, when these laws have been tested repeatedly by our brightest minds, when we observe they are consistent with nature whether peering at the infinitesimal through a microscope or across the galaxy through a telescope, that is what makes science worthy of celebration.

[1] Thomas Hobbes, Problematica Physica, 1662 (translated in English in 1682 as Seven Philosophical Problems) pp. 36-39, 146-148.
* This post first appeared here on 7 January 2015.