120

F >g. 13-

Fig. 14 .

Of the Air-Pump.

that the air above the quicksilver,ih the bottle will be confined there/because it cannot get out about the joinings, nor can it be drawn outthrough the qüicksilver into the tube. This tube is also open at top,and is to be covered with the receiver G and large tube E F, whichtube is fixed by brass collars to the receiver, and is dose at the top.This preparation being made, exhaust the air both out of the receiverand its tube; and the air will by the fame means be exhausted out ofthe inner tube BC } through its open top at C; and as the receiverand tubes are exhausting, the air that is confined in the glass bottleA will prefs so by its spring upon the surface of the qüicksilver, as toforce it up in the inner tube as high as it was raised in the ninth ex-periment by the pressure of the atmosphere: which demonstrates thatthe spring of the air is equivalent to its weight.

21. Screw the end C of the pipe C D into the hole of the pump-

plate, and turn all the three cocks d , G, and H, so as to open theCommunications between all the three pipes E, F, DC , and the hollowtrunk Then, cover the plates g and h with wet leathers,

which :have holes in their middle where the pipes open into the plates;and place the dose receiver I upon the piate g : this done, sliut thepipe F by turning the cock H, and exhaust the air out of the receiverI. Then, turn the cock d to sliut out the air, unscrew the machinefrom the pump, and having screwed it to the wooden foot L, put thereceiver K upon the piate h ; this receiver will continue loose on thepiate as long as it keeps füll of air; which it will do until the cock Hbe turned to open the communication between the pipes F and E,through the trunk A B ; and then the air in the receiver K, having no-thing to act against its spring, will run from K into I } until it be so divid-ed between these receivers, as to be of equal density in both ; and thenthey will be held down with equal forces to their plates by the pressureof the atmosphere; though each receiver will then be kept down butwith one half of pressure upon it, that the receiver I had, when itwas exhausted of air; because it has now one half of the common airin it which filled the receiver K when it was fet upon the piate; andtherefore, a force equal to half the force of the spring of commonair, will act within the receivers against the whole pressure of thecommon air upon their outsides. This is called transferring the airout of one vessel into another.

22. Put a cork into the square phial A, and fix it in with wax orcernent; put the phial upon the pump-plate, with the wire cage Bover it, and cover the cage with a dose receiver. Then, exhaust theair out of the receiver, and the air that was corked up in the phial

will