380 Inquiries inio the Laws of Dilatation of Solids, &c. 



The results which we have made known inform us that the 

 dilatation of t'le niercurv in the thermonieter follows a more 

 rapid comse than that of tiie air ; so that, if we regard the latter 

 as necessary to serve for the exact measurement to the tem- 

 peratures, we ought to conclude that the indications of the mer- 

 curial thermometer are too hiszh in the temperatures superior to 

 that of boiling water, and the numbers which we have given 

 might serve to make these indications undergo the proper cor- 

 rections. Those numbers increase besides in a sufficiently re- 

 gular manner, in order tiiat vve may without sensible error de- 

 . termine the correction relative to the temperatures intermediate 

 to those which are comprehended in the table. 



This conclusion destroys a doubt which was raised with re- 

 spect to the law of dilatation of the gases. This law had not 

 been announced in the same way by Messrs. Gay Lussac and 

 Dalton, whose experiments on the subject now before us ap- 

 peared at the same period. The experiments of M. Gay Lussac 

 proved that the dilatation of t!ie gases referred to the mercurial 

 thermometer is for each degree a constant fraction of the volume 

 at a determinate temperature. Mr. Dalton, on the contrary, 

 supposed tliat the increase of the volume is for each equal varia- 

 tion of ten)]jerature, a constant portion of the voliune at the 

 foregoing temperature. In truth, ?.Ir. Dalton does not appear to 

 have made direct experiments on this head : the only arguments 

 which he advances in favour of his hypothesis are reduced to the 

 extreme simplicity under which laws in appearance very complex 

 will then be presented, such as the law of the cooling of bodies, 

 and that of tlie variation of the elastic force of steam. 



Vv'e ascertained, however, that the first of those laws will by- 

 no means assume a character so simple as he pretends, even ad- 

 mitting his hypothesis to be correct. 



To conclude: It is not by considerations of this kind that we 

 can establish laws which observation alone ought to fiunish. 

 The experiments which we have made at high temperatures 

 compietel V destroy the hypothesis of the English experimentalist : 

 for, so far from these experiments polntrng out any thing per- 

 fectly positive as to the measurement of temperatures, it is at 

 least very probable that the march of the mercurial thermometer 

 ought to be more rapid than that of the temperatures, since in 

 all the other liquids the dilatability increases in proportion as 

 they are heated ; whereas in the hypothesis which we are at- 

 tacking, we shall find, on the contrary, that the dilatability of the 

 mercury decreases rapidly in proportion as it is heated; a re- 

 sult completely opposite to the very principles on which Mr. 

 Dalton had founded his theory of the measurement of tempera- 

 tures, [i^^ fjc continued.] 



LXXVIII. No- 



