123

Pneumatics.

0 f corpuscular Attraction, are0ll §iy repell’d from those Bodies ; this Re-pellency

He*

9 ls 0 ,,6 er >erally find it is in moist rainy Weather; andv ie r § at h must oftner be in this light than in a hea-? ti 0tl ta te : And that Instrument which shews the Vari-% e ^°‘the Air’s Gravity, or its different Weight at*Wr e nt Times, is call’d a Barometer, of whichvarious Kinds, which are here described ; butQf tst gi ve an Account of the most simple Struc-A Cllaf of those Instruments, which is as follows.

' fill 1 / Tube , hermetically seal’d at one End, is toAi r . ^th Quicksilver, well defecated and purged ofj 11 iijj ' /he Finger being then placed on the open Endp ,* a te Contact with the Mercury, so as not theog/f^ 6 of Air is admitted, the Tube is inverted,Mid i^ fully immersed with the Finger on the open'•pojj a Bason of the same prepared Mercury ; then• Roving the Finger, the Mercury in the Bason'et c j^ lri that in the Tube; and the said Column ofy >n the Tube will be seen immediately to sub-Ttth e ^ 'hie'down to a certain Pitch or Altitude, if the4 . I 6 ab °ve 3I Inches long, as it ought to be.

be such a Tube of 34 Inches Length,

]' S ^Ur ari Inch in Diameter, (as it ought to be forj^Cr^se) hermetically seal’d at A, and open at B ;u e the Bason of Mercury, in which the Tubet 5 ^asn Everted,

F ^derm/A ’ and

as s 11 ^’ tba ' ; T till this could be perform’d inas tbe Tube was inverted, all the Mer-till ^ i(. ue seend into the Bason, because as a heavyn it tend towards the Centre of the Earth,

limits M some Obstacle, as the Bason, to ob-l n ^f^n, and support it. I say, all this would

t/^'ube unless we can suppose any Power in

■tty n. tufiici, - - ~ -

>ill

fye,

the Surface of the Mercury inm the Tube GH. Now, ’tis easy

cient to sustain the Column of Mercury ;ca n be no such Power but that of Cohesion,iu Tubes of a small Bore, has beenbut in so large a Bore, as wesuppose

Hie?'**

■Sd a K, deed >

a “ ,e to sustain it ;

PlateXXVII.Fig. 4.