Over two months after it was written, this letter was noted at the regular weekly meeting of the Royal Society on March 24 / April 3 (O.S./N.S.; Birch's History, vol. IV p. 468, 470, 479):
Mr. Lodwick was desired to translate a letter of Mr. Leeuwenhoeck's, containing his microscopical observations upon cinnabar and gun-powder.
A week later, Lodwick had done as desired and the letter was read in a discussion of exploding gunpowder.
At their next weekly meeting on March 31 / April 10, 1686, the members spent some time discussing how gun-powder exploded. They tried a live demonstration, which did not work, perhaps fortunately.
Dr. Papin shewed his experiment of firing gun-powder in vacuo; but it not succeeding by reason of some soot got in with the powder, it was ordered to be tried again at the next meeting.
Robert Hooke was ready to step into the breach:
Mr. Hooke gave an account of his firing gun-powder in vacuo with a burning-glass; and said, that now and then a single corn would go off upon the whole heap without kindling the next corn; and that at length having melted the heap into a lump, it went off after the manner of the pulvis fulminans with a very great report, and burst his glass into a thousand pieces, and stuck great part thereof into the cieling.
Having set the scene, they turned to Leeuwenhoek.
Part of a letter of Mr. Leeuwenhoeck was read, containing several curious observations on cinnabar and gun-powder, and mentioning an experiment, proving the expansion of gun-powder to be into a space above 2000 times greater than the space, which it takes up before fired; for that a grain weight of powder containing 13 corns takes up as much room, when fired, as 2080 grains of water.
Dr. Papin had a different experience.
Three papers of Dr. Papin were read relating to his experiment of firing gun-powder in vacuo; in one whereof he said, that by the experiment made after the last meeting was over, he found, that 9 grains of gun-powder produces as much air, as fills the space of a third part of a pound of water; from whence he concluded, that 9 grains of powder yields 2 1/3 grains of air: and from hence it would follow, that each grain gives but 213 times as much air as its own bulk; which is far short of Mr. Leeuwenhoeck's experiment.
The note that followed was probably added later by Hooke:
N. B. That air being but about x/x00 [ed: illegible] of the weight of water, which is near the weight of gun-powder, a grain of gun-powder, if it should be turned into air, could take up but 800 times as much space as its own bulk. Wherefore either the observation of Mr. Leeuwenhoeck is faulty; or else the air produced by the explosion of gnn-powder has a greater elasticity than the common air in a lighter body.
The discussion ended when Edmond Halley brought out some shells, but Thomas Henshaw had the last word, at least for that day:
Mr. Henshaw was of opinion, that the constituent parts of the air are no other than the steams and exhalations out of the earth.
Even though Leeuwenhoek's next letter had arrived and been translated and read, at the meeting of April 21, the discussion returned to Leeuwenhoek's gunpowder experiments.
Part of a letter of Mr. Leeuwenhoeck was read, wherein he described the particles composing cinnabar, shewing them to be made up mostly of hexagonal figures, yet not without the mixture of some sulphureous and saline particles, whose figures, as viewed in his microscope, he described.
They weren't finished with this topic yet. A week later, they heard even more about Leeuwenhoek's investigations of gunpowder.
Part of a letter from Mr. Leeuwenhoeck was read, containing his observations upon the figure of the parts of the nitre after the explosion of the gun-powder; with several curious remards about the manner of firing gun-powder, about the quantity of air produced by the blast, and about the length of a cannon to carry farthest.
Whether there was further discussion is not reported in Birch's History. The next paragraph notes the arrival of not just a letter, but a long manuscript:
Dr. Vincent presented to the Society a manuscript treastise intitled, Philosophie Naturalis principia mathematica, and dedicated to the Society by Mr. Isaac Newton, wherein he gives a mathematical demonstration of the Copernican hypothesis as proposed by Kepler, and makes out all the phaenomena of the celestial motions by the only supposition of a gravitation towards the center of the sun decreasing as the squares of the distances therefrom reciprocally.
The Royal Society printed this book the following year, title page on right.