Pneumatics.

The Spring of the Air is demonst^by various Experiments: As, (i.) By 1 {

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the Air-Bubbles contract, subside, and retire with' 1 *-^Pores of the Fluid. In the fame Manner Soap-^ aYeast, £sY. will rife in a Head.

EXPERIMENT XVI. f >

16 .The Sixteenth Experi ment is exhibiting tkePhœf pief Boiling Water in the exhaujled Receiver. To this Pjthe Water must be as hot as the Finger can wct' V ftwhen put under the Receiver. Upon exhausting ^Air-Bubbles will be seen to rife very soon, and (ivery small; they soon appear bigger, and at last .jClarge, and rife with such Rapidity, as greatly to ftthe Water, and cause it to appear in all the Circum# 3 ..^of Boiling; which Agitation of the Water will coH 11 'j

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on which all the Wrinkles disappear, and t ^ e j e [i' 1 'puts on a youthful Face, till the Air be.again ftfwhen it instantly returns to its former State o*and fhrivel’d Countenance. ,

EXPERIMENT XVIII. u //f18. The Eighteenth Experiment exhibits the

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till the Air be let in again, and then it will cease,all will be quiet and still as at first. Some People *^ e ,gine the Water grows hotter by boiling under the ^reiver, as it does over the Fire; not consideringWater boils only by the great Expansion and R^ fttion of the Air it contains, from whatever Cause ^Jftceeds, as from the Heat of Fire, from takingPressure of the Atmosphere by the Air-Pump, ^ 'EXPERIMENT XVII.

17. The Seventeenth Experiment stews, thatApple will be plums d out, and made to look fatfi - S ftthe exhaujled Receiver. The Reason of whichExpansion of the Air in the Substance of the AP Jwhen the Pressure is taken off from its Surfa ce ’ ftthough some Parts of the Skin be pervious toeluded Air, (as appears by the little Streams rising ftthe Pores of the Apple placed in Water)greatest Part of the Surface is not, and will not ^ c ffore suffer the Air to pass out, but will yieldpand to its utmost Dimensions, (and sometim eS ^