183

Of the Air-Pump.

push down the wire P P (through the coller ofleathers in the neck q) upon the slider; whichwill disengage it from the pins, and allow thewills to turnround by the impulse of the spring:a nd as there is no air in the receiver to make anysensible resistance against them, they will bothwove a considerable time longer than they didw the open ait; and the moment that one stops,other will do so too.—This sinews that airwsislz bodies in motion, and that equal bodiesnteet with different degrees of resistance, accord-ing as they present greater or less surfaces to theai >', in the planes of their motions.

2. Take off the receiver M, and the mills; 4.

an d having put the guinea a and feather h uponthe brass slap c, turn up the slap, and so ut it intothe notch d . Then, putting a wet leather overthe top of the tall receiver AB (it being open bothat top and battom) cover it with the plate C,from which the guinea and feather tongs ed willthen hang within the receiver. This done, pumpthe air out of the receiver 5 and then draw upthe wire/a little, which by a square piece on itssower end will open the tongs ed-, and the slapfalling down as at c, the guinea and feather willdescend with equal velocities in the receiver ;an d both will fall upon the pump-plate at thefame instant. N. B. In this experiment, theobservers ought not to look at the top, but at thebottom of the receiver; in order to fee the gui-nea and feather fall upon the plate : otherwise,on account of the quickness of their morion, theyescape the fight of the beholders.

N 3

II. To