upon Gun-powder^ &c 0 231 
the bottom of the chamber further from, or bringing it nearer 
to, the vent, in order that the fire might be communicated to 
the powder in different parts of the charge. 
b , reprefent the lower part of the barrel. 
c, is the breech-pin, which is perforated with a hole four- 
tenths of an inch in diameter, the axis of which coincides 
with the axis of the bore. 
Into this hole the fcrew b 9 n> about four inches in length, is 
fitted ; to the end of which, n i that pafles up into the bore, is 
fixed a pifton 0, p b which, by means of collars of oiled leather, 
is made to fit the bore of the piece very exactly. The end of 
the pifton p, neareft the muzzle, is of brafs, and forms a move* 
able bottom to the bore, which by turning the fcrew h , by 
means of the handle m , is brought nearer to, or removed fur* 
ther from, the fixed vent v 9 by which means the powder is 
lighted at any aflignable diftalice from the bottom of the charge. 
But the length of the bore being altered by moving the 
pifton, which occafioned a fmall inaccuracy, and fome incon- 
venience attending the apparatus, it was laid afide, and ano- 
ther reprefented by fig, was fubftituted in the room of it. 
a , b 9 is a feftion of part of the barrel as before, and c is the 
breech-pin, which being perforated with a fmall hole through 
its center receives the fcrew/i g 9 which is about two-tenths of 
an inch in diameter, and four inches long. This fcrew being 
perforated with a very fmall hole, ferves to convey the fire into 
the chamber of the piece* and by fcrewing it further up into 
the bore, or drawing it backwards, the fire is communicated to 
different parts of the charge. 
But this method being found to he not intirely free from mac- 
curacies and inconveniencies, a third was fubftituted in the 
2 I % ' room 
