■2j2 Mr. Thompson’s Experiments 
trials, that the velocities of like mujket bullets, when they are 
diicharged from the fame, piece, by different quantities of the 
lame kind of powder, are. very nearly in the ful>duplicate 
ratio of the weights of the charges. Whether this law will 
hold good when , applied to cannon balls, and bomb {hells of 
large dimenfions, I dare not at prefent take upon me to decide ; 
but, for feveral reafons that might be mentioned, I am rather 
of opinion, that it will not ; at lead: not with that degree of 
accuracy which obtained in thefe experiments. 
Of the effect of placing the vent in different parts of the charge* 
There have been two opinions with refpefl: to the manner in 
which gun-powder takes fire. Mr. robins fuppofes that the 
progrefs of its inflammation is fo extremely rapid, u that all 
66 the powder of the charge is fired and converted into an elaftic 
u fluid, before the bullet is fenfibly mov^d from its place;” 
while others have been of opinion, that the progrefs of the in- 
flammation is much flower, and that the. charge is feldom or 
never completely inflamed before the bullet is out of the gun* 
The large quantities of powder that are frequently blown 
out of fire arms un-inflamed, feem to favour the opinion of 
the advocates for the gradual firing ; but Mr. robins endea- 
vours to account for that circumftance upon different principles, 
and fupports his opinion by fhewing that every increafe of the 
charge within the limits of practice produces a proportional 
increafe of the velocity of the bullet, and that .when the pow- 
der is confined by a great additional weight, by firing two or 
more bullets at a time inftead of one, the velocity , is not fenfi- 
bly greater than it ought to be according to his theory. 
