384 On the CONTRACTION 



in explaining many curious appearances that prefented them- 

 felves in his experiments upon the condudting power of fluids, 

 and in accounting for certain remarkable natural occurrences. 

 The Count, with his ufual ingenuity, has endeavoured to point 

 out the important purpofes which this peculiarity ferves in the 

 economy of nature, and to aflign the final caufe of fo remark- 

 able an exception from a general law. 



In recording the obfervations and opinions that have been 

 publiflied concerning this point, I might now, in order, notice 

 thofe of Mr Dalton of Manchefter, related in the fifth volume 

 of the Manchejler Memoirs, which tended to confirm and enlarge 

 our knowledge of it. But as Mr Dalton himfelf has called in 

 queflion the accuracy of the conclufions which had been drawn 

 from his experiments, and from thofe of preceding obfervers, I 

 fhall only remark, that they are of the fame nature, and nearly 

 to the faiue purport, as thofe of M. de Luc. 



It was in confequence of a communication with which Mr 

 Dalton favoured me, three months ago, that my attention was 

 direded to this fubjed. He informed me, that after a long train 

 of experiments he was led to believe that he, and his predecelTors 

 in the fame field of inveftigation, had fallen into a miflake with 

 regard to the contradlion of water by heat, and its expanfion by 

 cold, in confequence of overlooking or underrating the effedt 

 ■which the change in the capacity of the thermometei--fliaped ap- 

 paratus employed, muft occafion on the appai'ent volume of the 

 fluid. He ftated, in general terms, that on fubjeding water to 

 different degrees of temperature, in inftruments made of differ- 

 ent materials, he found the point of greateft denfity was indica- 

 ted at a different temperature in each. 



In an apparatus, having a ball of earthen-ware, it was at the 

 34th degree ; of glafs at the 42 d ; of brals at the 46th ; and of 

 lead at the 50th. And as water could not follow a different law, 

 according to the nature of the fubilance of the inftrument, he 



conceived 



