TRACT 37,

OF GUNNERY.

SOJ

greater difference takes place among the effects of the dif-ferent charges, with each of the guns, as in each case thereis a pretty uniform increase with the charge of powder; acircumstance which probably happens from the greater de-gree of heat likely to take place with the greater quantity ofpowder, and -which may therefore very well account for thedifferences here adverted to. So that all the numbers, nowfinally deduced, seem to possess all the favourable appear-ances that might be expected to happen from the causes mostlikely to produce such effects.

176. Let us now advert to other consequences resultingfrom the foregoing conclusions. We have found the strengthof inflamed gunpowder, when fired, or while the flame occu-pies only the same space as the powder did before it wasfired, on a medium to be about 2000 times the elasticity ofcommon air, or 2000 times the pressure of the atmosphere,when the barometer stands at 30 inches, that is, equal to theweight of a column of mercury, of equal base, and of theheight of 60000 inches, or 5000 feet, being almost a mile inheight; that is, including the effect of the heat of the flame.Now, it has been shown by Mr. Robins, and several otherphilosophers, that the elastic air generated by the firing ofany parcel of gunpowder, when cooled to the temperatureof common air, and made to fili a space of about 244 timesgreater than the bulk of the powder, was then reduced ex-actly to the same strength or elasticity as common air; and.that therefore, when cooled, and filling only the first spaceof the unfired powder, the elasticity being at least in as higha proportion as the density, its elasticity must be then equalto 244 times that of natural air. And having found that aheat equal to that of red-hot iron, will increase the elasticityof air 4-jtj. times; therefore, supposing the heat of inflamedgunpowder to be equal to that of the red-hot iron, he con-cluded that the elasticity of the heated elastic fluid.would be'equal to 244 x 4 T * T or 998 times, or in round numbers about1000 times, greater than that of the atmosphere.