VOL. XXIV.] PHILOSOPHICAL TRANSACTIONS. 2/1 



iron frame, which hold the great wheel d, 23 inches diameter, within its 

 groove; E the brass plate of the air pump, on which the recipient ff is placed 

 gg the spindle, to which bodies of different sizes may be fastened, by a hole 

 passing through the middle of them, sufficient to receive the spindle; and by 

 means of the 2 nuts, hh, a larger or a srnaller body may be screwed fast between 

 them; ii a brass plate, turned true to the ground edge of the recipient, on 

 which it is placed, having a brass box in the middle, full of collars of leather 

 well oiled, through which the spindle passes, the hole of the brass being also 

 just fit to receive it ; kk two pillars with nuts, to screw down a piece of board, 

 which has an iron fastened to it to receive the upper point of the spindle, the 

 lower one falling into a brass socket, screwed to the middle of the plate of the 

 air pump ; 11 the supporters, reaching from the upper board of the ladder to 

 the pillars, to prevent the recipient's being drawn from its place by the motion 

 and tug of the wheel-band; mm the small wheel which the band surrounds 

 from the great one, and is 1 inch and a half diameter; nn the winch which 

 gives motion to the whole, the small wheel mm making about 15 revolutions 

 to one of the large wheel d ; so that a body fastened to the spindle gg, of the 

 small wheel m, must be turned 15 times round to once of the great wheel; 

 and accordingly as it shall exceed in diameter the small wheel, so will the velocity 

 of the motion of the extreme parts be proportionably increased ; oo are two 

 screws, which fasten the ladder to the floor. 



ExPER. I. Showing that Light is producible on a swift Attrition of Amber 

 on IVoollen in Vacuo. — Having prepared the machine above described, for 

 giving a swift motion to bodies in vacuo, the amber made use of was beads, 

 about the size of small nutmegs, and threaded; by which means a piece of 

 wood was surrounded with them, which I had purposely caused to be turned, 

 with a groove on the edge, to keep the beads from being displaced on a smart 

 attrition; and between every bead a string was tied over from pin to pin, which 

 were so many pieces of small wire, driven through the wood, for their better 

 security, the beads appearing about half their diameter beyond the wood to 

 which they were fixed, as in fig. 23. In this manner it was put on the spindle, 

 and fastened there by the two nuts, before described, as in fig. 24. Then 

 the brass plate on which the woollen was wrapped, being screwed to its place, 

 (by means of the socket, which receives the lower point of the spindle) would 

 then spring back, and embrace the amber with a moderate force, as in fig. 24. 

 Thus prepared, and the receiver placed over, with its upper plate and box for 

 the spindle to pass through, the pump was worked, and in a very little time 

 the mercury in the gauge was elevated to about 29 inches and a half, which 

 showed the recipient was well exhausted of its air. The large wheel being then 



