346 ® n l k e txpavfive Force of the Steam oj 'Water y 

 invention of them down to the mod recent difcoveries, t 

 recur to the labours of Bettancourt, which I have explained 

 at full length, as well as the application that may be made of 

 it to phyfics and the arts *. I refer thofe, who may be de- 

 firous of being thoroughly acquainted with the fubjec~t, to 

 that work, and mall here content myfelf with giving an idea 

 of the apparatus. 



The fluid with which the experiments were made was 

 confined in a very ftrong boiler made of copper, being eight 

 inches at its greateft diameter, and fourteen inches in height. 

 The upper part of it was clofed by a cover made of copper 

 alfo, through which pancd three tubes. The ftrft ferved to 

 introduce the fluid into the boiler, and could be clofely fhut 

 by means of a fcrew. The fecond was occupied by a ther- 

 mometer, having its ball about two inches above the bottom 

 of the boiler, and the feaie, which was on the outfide, con- 

 tained from o to no" of Reaumur. To the third was 

 adapted a bent barometric tube, having two lines of internal 

 diameter, the afcending branch of which was no inches in 

 length. 



By means of a lateral ccck a communication was efta- 

 blifhed between the boiler and an air pump, which ferved to 

 make a vacuum before a fire was kindled in the furnace 

 below the apparatus. This circumftance of evaporation in 

 a vacuum, forms an effential difference between the experi- 

 ments of Bettancourt and thofe made before by Ziegler, and 

 renders them applicable to the theory of the fleam-engine, 

 where the vapour acts in a fpace freed from air. 



* In this fecond volume will be found experiments made on the fame 

 object, and communicated to me by their author John Henry Ziegler. 

 They were published at Baile in 1769, in a memcir entitled : Specimen 

 fhyjtco-cbemicum de tJigr/lore Papini, ejus Jiruclurd, effeclu et up, frimi- 

 tias experin-.entorum nevorum circa fiuidorum a colore rarrfatTtcmem et 

 vaporum elafticitatcm cxbibens. Bettancourt, who did not fee them till he 

 had rinhhed his own, mentions tliem m his memoir. It will be perctived, 

 by the account I have given of them, that they deprive him of none of 

 that glory whifh he has a right to espedt from his labours. 



