23 2 Mr. Thompson's Experiments 
room of it, which was found to anfwer much better than either 
of the preceding. 
The end of the bore was now firmly clofed by a folid breech- 
pin p, fig. 3. and three vent holes rn, n, and 0 , were made in 
the barrel; one of them, m, even with the bottom of the bore, 
and the other two at different difiances from it. Any two of 
thefe vent holes, as n and 0 for inflance, being clofed up by r 
folid fcrews, a perforated fcrew, or vent tube v, was fcrewed 
into the third, which ferved to contain the priming, and to. 
convey the fre to the powder lodged in the bore of the piece. 
Sometimes a longer vent- tube, reprefented by fig, 4. was- 
made ufe of ; which, pafling through the powder in the cham- 
ber of the piece, communicated the fire immediately to that 
part of the charge that lay in the axis of the bore. 
Another vent-tube alfo was ufed occafionally, which differs 
in many refpefls from both thofe that have been defcribed. It 
is fo con {huffed as to convey the fire to the charge ; but, as foon 
as the powder in the chamber of the piece begins to kindle, 
and the elaffic fluid to be generated, the vent is firmly clofed by 
a valve, and no part of the generated fluid is permitted to^ 
efcape. This I fhall call the valve-vent , and it is reprefented 
by fig. 5. upon an enlarged fcale, that the parts of it may 
appear more di {finch 
a, b, is a longitudinal feffion of a fmali portion of the folid: 
fide of the barrel. 
Cy d, is the vent-tube, which is in all refpe&s like the fliort 
vent- tube commonly made ufe of, except only that in this the 
end of the vent-hole (A) which goes into the chamber is en- 
larged in the form of the wide end of a trumpet or funnel. 
To this enlarged aperture the valve, v, is accurately fitted,, 
and by means of the fmall ftem or tail, /, which is fixed to the 
valve 3 
