He determines that the elasticity of air is augmented in a proportion somewhat greater than that of 4 to 1, when heated to the extremest heat of red-hot iron; and supposing that the flame of fired gunpowder is not of a less degree of heat, increasing the former number a little more than four times, makes nearly 1000; which shows that the elasticity of flame, at the moment of explosion, is about 1000 times stronger than the elasticity of common air, or than the pressure of the atmosphere. But, from the height of the barometer, it is known that the pressure of the atmosphere upon every square inch is on a medium of 14-3/4ths, and therefore 1000 times this, or 14750 lbs. is the force of pressure of inflamed gunpowder, at the moment of explosion, upon a square inch, which is very nearly equivalent to six tons and a half. This great force, however, diminishes as the fluid dilates itself, and in that proportion; viz. in proportion to the space it occupies, it being only half the strength, when it occupies a double space, one-third the strength, when a triple space, and so on. Mr. Robins further supposed the degree of heat above mentioned to be a kind of medium heat; but that in the case of large quantities of powder the heat will be higher, and in very small quantities lower; and that therefore in the former case the force will be somewhat more, and the latter somewhat less, than 1000 times the force of the atmosphere. He further found, that the strength of powder is the same in all variations in the density of the atmosphere: but that the moisture of the air has a great effect upon it; for the same quantity which in a dry season would discharge a bullet with the velocity of 1700 feet in one second, will not in damp weather give it a velocity of more than 12 or 1300 feet in a second, or even less, if the powder be bad, or negligently kept. _Robins's Tracts_ vol. i, p. 101, &c. Further, as there is a certain quantity of water, which, when mixed with powder, will prevent its firing at all, it cannot be doubted but every degree of moisture must abate the violence of the explosion; and hence the effects of damp powder are not difficult to account for. The velocity of expansion of the flame of gunpowder, when fired in a piece of artillery, without either bullet or other body before it, is prodigiously great, viz. 7000 feet per second. But Mr. Bernoulli and Mr. Euler think it is still much greater.