30#

THEORY And practice

TRACT 37.

water; which may well be considered as probably the great-est degree of compression that air is capable of. Hence itmay be perceived that a prodigious force must be exerted bynature in generating nitre: and as this great force actuallyexists in nature, it is very probable that the air in the nitreis thus compressed into the most dense state possible; andin this consists the similitude among the different particlesof nitre.

ISO. It remains now then to determine the velocity withwhich the elastic flame expands itself and moves. If thewhole substance of the powder was changed into an elasticfluid at the instant of the explosion, then, from the knownelasticity of this fluid deduced from our experiments, in theforegoing articles, and its known density, we might deter-mine the velocity with which it would begin to expand, andcould thence discover its future augmentations in its pro-gress through the gun cylinder. But, as it is probable eventhat the powder does not inflame all at once; and as it iscertain that the greatest part of it, viz. consists of grossmatter not convertible into an elastic fluid ; which matter willin the explosion be mixed with the elastic part, and will byits weight retard the activity of the explosion, and yet theywill not be so uniformly mixed, and intimately united, as tobe moved with one common motion; but the gross part willbe less accelerated than the elastic, and some of it will noteven be carried out of the barrel, as appears by the quantityof unctuous matter which adheres to the inside of all fire-arms, after they have been discharged. And besides, it ap-pears not that even the elastic fluid itself is uniformly diffusedthrough all the space of the gun cylinder; but rather, onthe contrary, that the elastic fluid must be more compressedand dense in the after parts, and less in front. From allthese circumstances it is manifest that some uncertainty mustattend even the application of any theorem to our best ex-periments, such as the preceding formula v = 46'7r 1,0 P + w

X log. —} for the value of the ultimate velocity c, or the