upon Gun-powder , &c. 241 
as the joifts upon which the floor over head was laid afforded a 
firm and commodious fupport for fufpending the pendulum and 
the barrel, and the walls and roofs of the building ferved to 
fcreen the apparatus, which otherwife might have been difcom- 
pofed by the wind, and injured by the rain and dews. A pair 
of very large doors, which formed the whole of one end of 
the room, were kept conffantly open during the time the 
experiments were making, in order to preferve the purity of the 
air within the houfe, which otherwife would have been much 
injured by the fmoke of the gun- powder ; and that, in all pro- 
bability, would have had a confiderable effect in leflening the 
force of the powder, and vitiating the experiments. In order 
ftill further to guard againft this evil, the barrel was placed as 
near as poftible to the door, and the pendulum was hung up at: 
the bottom of the room. 
Fig. 1 2. reprefents the apparatus as it was put up for making 
the experiments. 
a r b , is the barrel with its carriage, fufpended by the pendu- 
lous rods c, and 
R, is the ribbon which ferved to meafure the afcending arc 
©f its recoil* 
P, is the pendulum, and 
r, the ribbon that meafured the' arc of its vibration. 
The diftance from the mouth of the pieOe to the pendulum 
was juft 1 2. feet.. 
A table 
