134 ON THE EXPANSION OP EEASTIC FLUIDS. 



fideration whether the mercurial thermometer is an accurate 

 meafure of the increments of heat ; if it be, the hypothefis 

 fails ; but if equal increments of heat caufe a greater expan- 

 fion in mercury in the higher than in the lower temperatures, 

 and that in a fmall degree, the facl noticed above inftead of 

 being an objection will corroborate the hypothefis. — Dr. Craw- 

 ford determines the expanfions of mercury to be very nearly 

 in proportion to the increments of heat : M. De Luc makes 

 them to be lefs for a given quantity of heat in the lower than 

 in the higher part of the fcale ; and in a ratio that agrees with 

 this hypothefis. Now as every other liquid we are ac- 

 quainted with is found to expand more in the higher than in 

 the lower temperatures; analogy is in favour of the conclu- 

 fions of De Luc, that mercury does the fame. 



Luflac. 



His method. 



Short account of j n the Bulletin des Sciences, there is a notice of a memoir 

 by Mr. Gay °^ ^it. ^ay Luflac on the dilation of the gafes and vapours ; 

 and the memoir itfelf is given in the A3 d volume of the Annals 

 de Chemie, whence I (hall, as early as convenient, give either 

 a full abftract or a tranflation. This able author gives the 

 fame conclufion as that of Mr. Dalton, and, like him, attri- 

 butes the errors of preceding experimenters to the humidity 

 of the gafes they examined. 



His experiments were made by expelling the gas from a 

 glafs ball properly fitted up, and determining the expanfion 

 by weighing the apparatus, after water had been fuffered to 

 come in during the cooling, to occupy the fpace of the ex- 

 truded gas. He very candidly informs us, that Cit. Charles 

 had deduced the general refult of the equal and fimilar expan- 

 fion of all the gafes by heat, under like prefTure, fifteen years 

 before, though he did not publith it ; and he gives an hiflorical 

 account of the labours of his predeceffors ; fo that we muft 

 neceffarily conclude that he could not have feen the late pub- 

 lication of the Manchefter Society, in which the extenfive re- 

 fearches of Mr. Dalton are inferted ; and wherein it appears 

 that the preceding memoir was read about a year before that 

 of Mr. Gay Luflac was read to the Inftitute. The French 

 Philofopher finds the expanfion or increafe of dimenfion, be- 

 tween the freezing and boiling water points, to be 0. 375* 



which 



Mr. Dalton's 

 experiments 

 ■were earlier. 



