Previously to the researches of Robins, the theory of atmospheric resistance was but imperfectly surmised, and when he made his statements of the immense resistance which the fluidity of the air offered to projectiles in a high state of velocity, they were treated as the idle chimeras of a speculative brain; and yet he only was enabled to estimate the real effect of the explosive nature and force of gunpowder to a very limited extent: indeed, so limited, that Hutton, only twenty years subsequently, speaking of Robins’ theory, says, “Mr. Robins and other authors, it may be said, have only guessed at, rather than determined. That ingenious philosopher, in a simple experiment, truly showed that, by the firing of a parcel of gunpowder, a quantity of elastic air was disengaged; which, when confined in the space only occupied by the powder before it was fired, was found to be nearly 250 times stronger than the weight or elasticity of the common air. He then heated the same parcel of air to the degree of red hot iron, and found it in that temperature to be about four times as strong as before; whence he inferred, that the first strength of the inflamed fluid must be nearly 1,000 times the pressure of the atmosphere. But this was merely guessing at the degree of heat in the inflamed fluid, and, consequently, of its first strength; both which in fact are found to be much greater. It is true that this assumed degree of strength accorded pretty well with that author’s experiments; but this seeming agreement, it might easily be shown, could only be owing to the inaccuracy of his own further experiments; and, in fact, with far better opportunities than fell to the lot of Mr. Robins, we have shown that inflamed gunpowder is about double the strength that he has assigned to it, and that it expands itself with the velocity of about 5,000 feet per second.” On the same subject he further says:--“On this principle it was that Mr. Robins made all his experiments and performed all his calculations in gunnery. But it is manifest that this method of guessing at the degree of heat of the flame must be very uncertain and unsatisfactory, being much below the truth; since all our notions and experience of the heat of inflamed powder convince us that it is higher than that of red hot iron, and, indeed, it has clearly appeared from our experiments, that its heat is at least double that of red hot iron, and that it increases the elasticity of the elastic fluid more than eight times.”