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will varioufly alter every term in thefe ferics, and produoe 

 other feries, the terms of which will continually apprcximate 



to 



would be ftill more deficient If tlie mere'' were poured cold into the tube. Now 

 fuppofing the altitude of the mere' in the ftandard to be thirty inches, -^^^jths of 

 an inch is the i 200th part of the whole ; and if the mere' in the gage be as high 

 as that in the ftandard, the rarefaftion is only 1200; and that in the ordinary Torri- 

 cellian tube, is, I believe, never greater, but moft commonly lefs than this; though 

 from tliere being no air bubble apparent at the top of fuch a tube, when on inclining 

 it the mere'' afcends, one might imagine that no claftic fluid reded above the mer' : 

 for if the tube be fdled cold, there will be moifture williin it, which will be con- 

 denfed into fmall invifible particles by the preflure of the atmofphere when the tube 

 is inclined, but will expand, again in elaftic vapour, depreffing the mere'', when bv 

 placing the tube vertical, that prefTure is removed : and when tlie tube is filled hot, 

 and fo has no moifture in it, an air-bubble will in the fame circumttances be vifible. 

 This I found however to be partly difcharged, and the mere' to ftand higher in it, 

 by inclining the tube while in the ciflern (after it had flood perpendicular and the 

 mere' had funk to the natural altitude) until it had afcendcd to the top, and taking 

 it- full out of the ciltern, by clofing its end while immerfed in it, with my finder, 

 then having lliaken out a drop of mere'' to allow an air-bubble to be once moved 

 through it, this brought up with it moft part of the air which had been colledled in 

 one bubble at the top ; after which reftoring the drop which had been taken out, and 

 immerging it again in the ciftern, the mere'' flood in it higher than before, and I 

 believe from this management it would always do fo. This was done in the prefence 

 of Do£lor Young, who from his well-known zeal for the advancement of fcience, 

 wis pleafed to be prcfent at a trial of the pump's performance ; at which time it fo 

 fji exhaufted a rec as to raife the mere!" in the baromr-gage, near .^.'^th of an inch 

 iigher than it ftood at the highclt, in the barom'-tube here mentioned, of equal bore 

 with that of the gage, and ftanding parallel and perpendicular together in the fame- 

 ciilern. 



If there be in the rec no moifture nor vapour expanfible only in vacuo, the pear- 

 gage (as I have always found) will correfpond with both the baromr-gages ; and 

 ■when the rarefadlion is near 4000, the eye cannot diftinguifh the difference be-. 



tweerL 



