1

Of the Air-Putnp. 1S5

the air be let into it by turning the cock k ; andthen it becomes loose.

3- Set the little glass A B (which is open at Fig. 5.both ends) over the hole i upon the pump-plateand put your hand close upon the top of itat B : then, upon exhausting the air out of theglass, you will find your hand pressed down witha great weight upon it: so that you can hardlyPlease it, until the air be re-admitted into theglass by turning the cock k ; which air, by act-ing as strongly upward against the hand as thesternal air acted in pressing it downward, willrelease the hand from its confinement.

4- Having tied a piece of wet bladder b over Fig. 6.rhe open top of the glass A (which is also open atbottom) set it to dry, and then the bladder willbe tight like a drum. Then place the open endA upon the pump-plate, over the hole r, andbegin to exhaust the air out of the glass. Asthe air is exhausting, its spring in the glass willbe weakened, and give way to the pressure of theoutward air on the bladder, which, as it is pres-sed down, will put on a spherical concave figure,which will grow deeper and deeper, until thelength of the bladder be overcome by theWeight of the air-, and then it wili break with areport as loud as that of a gun-—If a flat pieceglass be laid upon the open top of this re-ceiver, and joined to it by a flat ring of wetleather between them-, upon pumping the air°ut of the receiver, the pressure ot the outwardair upon the flat glass will break it all topieces.

5* Immerse the neck c d of the hollow glass Fjg. 7.ball e 3 in water, contained in the phial a a-, thenfe it upon the pump-plate, and cover it and thehole i with the close receiver A-, and then beginN 4 to