60 Notices respecting New Booh. 



count all the circumstances, the dilatation of the bulb, that of the 

 tube, &c., the indication which the first of these thermometers would 

 give is identical with that which the second would give in the same 

 circumstances, provided that their reservoirs were of the same 

 capacity. 



Convinced by this analysis that he might employ indifferently 

 either form of the thermometer, M. Regnault, from the motives we 

 have already indicated, preferred the method of overflow, as sus- 

 ceptible of much greater exactitude ; the greatest losses which he 

 could perceive in his weighings never exceeded 3 or 4 milligrammes, 

 which is exceedingly inconsiderable for the temperatures to which 

 his experiments were carried. 



He tried in succession thermometers made with the flint-glass of 

 Choisy-le-Roi, with common glass, with green glass, and with 

 Swedish glass. He took care to have each kind of glass analysed 

 by a skilful chemist, and the analyses were made of the reservoirs 

 themselves of the thermometers. 



The flint-glass of Choisy-le-Roi always presenting exactly the same 

 composition, on account of the very particular care taken in the 

 manufacture, is uncommonly well-fitted for comparative experi- 

 ments. Three thermometers were prepared with this kind of glass ; 

 one had the reservoir made of a flint-glass tube about 14 millims. in 

 internal diameter, and this was soldered to a capillary tube of the 

 same glass ; the second was obtained by blowing a spherical reser- 

 voir on a capillary tube of flint-glass ; and the third was formed of the 

 same capillary tube worked in the lamp so as to produce a cylin- 

 drical reservoir. This last exhibited a rather larger proportion of 

 silica in the analysis, which was probably occasioned by the long 

 working in the lamp having driven off some of the other ingredients 

 of the glass by volatilization. 



Observed successively in their course, compared with air-ther- 

 mometers, the three mercurial thermometers, made of Choisy-le-Roi 

 flint-glass, proceeded in sensible agreement from 0° up to 325°, and 

 experiment showed that the same corrections may be applied to 

 them to bring their indications to those of the air-thermometer. But 

 though the law of dilatation did not differ in the glass of the different 

 thermometers, this was not the case with the absolute dilatation, which 

 was very different for each of the reservoirs, the first of which ex- 

 hibited a sensibly smaller coefficient of dilatation than the other two. 



Several thermometers constructed of common glass, but some 

 with cylindrical, others with spherical reservoirs, and some formed 

 of tubes or little globes soldered to capillary tubes, were in like 

 manner compared with the air-thermometers. It was found that 

 they differed considerably in their course from the thermometers 

 with flint-glass envelopes, and that these two kinds of thermometers 

 could not be regarded as comparable. The dilatations of common 

 glass between 0° and 100° varied in a very marked manner with the 

 difference of composition, and above all according to the manner in 

 which the glass had been worked. Now there are great differences 

 in the composition of common glass, which is not manufactured with 



