Os the Air-Pump.

will come out of both receivers; but the large one M will be fbrci-bly held down to the pump by the pressure of the external air; whilstthe small one O, having no air to press upon it, will continue loose,and may be drawn up and let down at pleasure, by the wire PP. But,upon letting it quite down to the piate, and admitting the air into thereceiver M , by the cock k, the air will prefs so strongly upon the smallreceiver O, as to fix it down to the piate ; and at the fame time, bycounterbalancing the outward pressure on the large receiver M, itwill become loose. This experiment evidently fhews, that the re-ceivers are held down by pressure, and not by suction, for the inter-na! receiver continued loose whilst the operator was pumping, and theexternal one was held down ; but the former became fast immediatelyby letting in the air upon it.

12. Screw the end A of the brass pipe AB F into the hole of thepump-plate, and turn the cock e until the pipe be open; then put awet leather upon the piate cd, which is fixed on the pipe, and coverit with the tali receiver G H, which is dose at top: then exhaust theair out of the receiver, and turn the cock e to keep it out; which'done, unscrew the pipe from the pump, and set its endyi into a’basonof water, and turn the cock e to open the pipe ; on which, as thereis no air in the receiver, the pressure of the atmosphere on the waterin the bason will drive the water forcibly through the pipe, and makeit play up in a jet to the top of the receiver.

iz, Set the square phial A (Fig. 14.) upon the pump-plate, andhaving covered it with the wire cage B, put a dose receiver over it,and exhaust the air out of the receiver; in doing of which, the airwill also make its way out of the phial through a small hole in its neckunder the valve b. When the air is exhausted, turn the cock belowthe piate, to re-admit the air into the receiver; and as it cannot getinto the phial again, because of the valve, the phial will be broke intoforne thousands of pieces by the pressure of the air upon it. Had thephial been of a round form, it would have sustained this pressure likean arch, without breaking; but as its fides are flat, it cannot.

Tv ß>ew the elaftkity or spring os the air.

14. Tie up a very small quantity of air in a bladder, and put itunder a receiver; then exhaust the air out of the receiver, and thelmall quantity which is confined in the bladder (having nothing to actagain st it) will expand itself so by the force of its spring, as to fili thebladder as füll äs it could be blown of common air. But upon

letting