2^8 Mr. Thompson’s Experiments 
the vent, fuch as diminiftiing the recoil, Increafing the force 
of the charge, & c. ; but the vent may be indifferently in any 
part of the chamber where it will beft anfwer upon other ac- 
counts : and there is little doubt but the fame thing will hold 
good in great guns, and all kinds of heavy artillery. 
Almoft every workman who is at all curious in fire -arms has a 
particular fancy with regard to the beft form for the bottom of 
the chamber, and the proper pofition of the vent. They in 
general agree, that the vent fhould be as low or far back as 
poffible, in order, as they pretend, to leflen the recoil ; but no 
two of them make it exactly in the fame manner. Some make 
the bottom of the chamber flat, and bring the vent out even 
with the end of the breech-pin. Others make the vent flanting 
through the breech-pin, in fuch a manner as to enter the bore 
juft in its axis. Others again make the bottom of the chamber 
conical ; and there are thofe who make a little cylindric cavity 
in the breech-pin, of about two-tenths of an inch in diameter, 
and near half an inch in length, coinciding with the axis of 
the bore, and bring out the vent even with the bottom of this 
little cavity. 
The objection to the firft method is, the vent is apt to be 
flopped up by the foul matter that adheres to the piece after 
tiring, and which is apt to accumulate, efpecially in damp wea- 
ther. The fame inconvenience in a ftill greater degree attends 
the other methods, with the addition of another, arifing from 
the increafed length of the vent ; for the vent being longer it 
is not only more liable to be obftrudled, but it takes a longer 
time for the flame to pafs through it into the chamber, in con- 
fequence of which the piece is flower in going off, or, a& 
fportfmen term it, is apt to hang fire. 
2 
The 
