^02 Mr, Thompson’s Experiments 
better, for the axis of the pendulous rods to reft upon level 
pieces of wood or iron, than for them to move in circular 
grooves : only care muftbe taken to confine them by ftaples or 
foine other contrivance,, to prevent their flipping out ol their 
places. 
The trunnions, by means of which, the barrel is connected 
\vith the pendulous rods, arid upon which it is lupported, 
fhould be as fmall as poffible, in order to leffen the friction ; 
and for the fame realbn they fhould be well polifhed, as well as 
the grooves that receive them.. They need not be caft upon the 
barrel, but may be fcrewed into it after it is finifhed. 
In making, the experiments, regard muft be had to the heat 
of the barrel, as well as to the temperature of the atmolphere ; 
for Jjpat and coljd^' drynefs and moifture, have a very fenfible 
effect upon gun-powder to increafe or diminifh its force. If 
therefore j a vsry great degree of accuracy is at anytime re- 
quired^ it wiljt tie heft to begin by firing the piece two or three 
tjpies iperely to warm it ; after which three or four experi- 
ments may be made witli ftandard powder, to determine anew 
..the,prppf mark (tor the ftrength of the fame powder is dif- 
fereiit upon different days) ; and when this is done, the experi- 
ment s v with th^: powder that is to be proved are to be made, 
taking care topreferve the fame interval of time between the 
firings., that the heat of the piece may be the fame in each 
trial. 
„ If ^11 ^ thefe precautions are taken,., and if the bullets are of 
the. fame weight and dimerifioiis, powder may be proved by 
, x this method with much greater accuracy than has hitherto been 
done by any of the. common methods, made ufe of for that 
gurpofe. 
