-oo Mr. Thompson’s Experiments 
adtions, whole operations have a contrary tendency, fo com pen- 
fate each other, that their effects when united are not fenfible. 
But when this is the cafe, if any one of the caufes of error is 
removed, thole which remain will be detected. 
When any given charge is loaded with a heavy bullet, more 
of the powder is inflamed in any very fhort fpace of time than 
when the bullet is lighter, and the adlion of the powder ought 
of courfe to be greater on that account ; but then a heavy bul- 
let takes up more time in palling through the bore than a light 
one, and confequently more of the elallic fluid, generated from 
the powder, elcapes by the vent and by windage. It may hap- 
pen, that the augmentation of the force, on account of one of 
thefe circumfhnces, may exactly counterbalance the diminution 
of it arifing. from the other; and if it fhould be found upon 
trial that this is the cafe in general, in pieces as they are now 
conftrudled, and with all the variety of ihot that are made ufe 
of in practice, it would be of great ufe to know the fact : and 
poflibly it might anfwer as well, as far as it relates to the art of 
gunnery, as if we were perfectly acquainted with, and were 
able to appreciate, the effedl of each varying circumftance under 
which an experiment can be made. But when, concluding too 
haftily from the refult of a partial experiment, we fuppofe 
with Mr. robins, that becaufe the flam total of the adlion or 
preffure of the elaft'ic fluid upon the bullet, during the time of 
its paflage through the bore, happens to be the fame when bul- 
lets of different weights are made ufe of (which colledlive 
preffure is in all cafes proportional to, and is accurately mea- 
fured by, the velocity, or rather motion, communicated to the 
bullet) that therefore the prelfure in any given part is always 
exadtly the fame, when the quantity of powder is the fame 
with which the piece is fired ; and from thence endeavour to 
prove ? 
