Experiments upon Gunpowder. 3 



of an inch in diameter, the axis of which perforation 

 coincides with the axis of the bore. 



Into this hole the screw /z, n^ about four inches in 

 length, is fitted ; to the end of which, ;z, that passes up 

 into the bore, is fixed a piston, <?, ^, which, by means of 

 collars of oiled leather, is made to fit the bore of the 

 piece very exactly. The end of the piston ^, nearest 

 the muzzle, is of brass, and forms a moveable bottom 

 to the bore, which by turning the screw h^ n, by means 

 of the handle m^ is brought nearer to, or removed 

 further from, the fixed vent v, by which means the 

 powder is lighted at any assignable distance from the 

 bottom of the charge. 



But the length of the bore being altered by moving 

 the piston, which occasioned a small inaccuracy, and 

 some inconvenience attending the apparatus, it was laid 

 aside, and another, represented by Fig. 2, was substi- 

 tuted in the room of it. 



<2, b, is a section of part of the barrel as before, and 

 c is the breech-pin, which, being perforated with a small 

 hole through its center, receives the screw f^ ^, which is 

 about two tenths of an inch in diameter, and four inches 

 long. This screw, being perforated with a very small 

 hole, serves to convey the fire into the chamber of the 

 piece, and by screwing it further up into the bore, or 

 drawing it backwards, the fire is communicated to differ- 

 ent parts of the charge. 



But, this method being found to be. not entirely free 

 from inaccuracies and inconveniences, a third was sub- 

 stituted in the room of it, which was found to answer 

 much better than either of the preceding. 



The end of the bore was now firmly closed by a solid 

 breech-pin, p^ Fig. 3, and three vent-holes, m^ Jt, and <?, 



