192 Petit and Ditlong on some important Points [Sept. 



but this condition was likewise fulfilled, for the body was always 

 plunged into a vessel, the sides of which were blackened inte- 

 riorly, and covered on all parts with a thick coating of melting 

 ice. 



To this first method of diminishing the rate of cooling, with- 

 out any diminution of the requisite accuracy, we added another, 

 the influence of which we could calculate from our knowledge of 

 the laws of the communication of heat. It results from these 

 laws that the velocity of cooling of a body may, ceteris paribus, 

 be considerably diminished when its surface possesses but a very 

 weak radiating power, and is plunged in an air very much 

 dilated. To realize these circumstances, we resolved to operate 

 upon solid bodies only in a state of very fine powder. In this 

 st ute they were contained, and strongly pressed into a cylindrical 

 vessel of silver very thin, very small, and the axis of which was 

 occupied by the reservoir of the thermometer that served to 

 point out the rate of cooling. This vessel was then placed in the 

 centre of the vessel ; and the air contained in it was dilated till 

 its tension did not exceed two millimetres ; and care was taken 

 to reproduce the same vacuum in each experiment. 



By the precautions just stated, we succeeded in making the 

 cooling of very small bodies exceedingly slow, and consequently 

 easy to observe with precision. To give an idea of the limit 

 which we have obtained in this respect, it may be sufficient to 

 say, that when we measured tin: capacities of the densest bodies, 

 such as gold and platinum, the masses on which we operated did 

 not exceed the weight of 30 grammes ; and that in the cases in 

 which the cooling was most rapid, its duration was not less than 

 15 minutes. 



It would now be requisite to give the formula which served for 

 the calculation of the observations ; but the details into which 

 we should be obliged to enter respecting the manner of making 

 the different corrections depending on the method of proceeding 

 would lead us into a discussion which we reserve for the publi- 

 cation of the definitive results of all the direct experiments which 

 we have made on the subject. We shall add only a single 

 remark, that having compared the specific heats thus obtained 

 for the worst conductors with those given by the method of 

 mixture, or by the calorimeter, the remarkable agreement has 

 afforded the most convincing proof of the accuracy of the process 

 which we have adopted. 



We shall now present in a table the specific heat of several 

 simple bodies, restricting ourselves to those results about winch 

 we entertain no doubt. 



