and the Mode of its Communication. 35 



observations (= 15 minutes), we were to determine by 

 computation the time when the instrument was at the 

 temperature of 84 (the lower point of the standard 

 interval of 10 degrees answering to the temperature of 

 the air, = 44, in which the instrument was cooled), it 

 will turn out, 8 minutes and 55 seconds after nh. 

 30 min. The observed time was nh. 39 min. ; which 

 differs from the computed time no more than 5 seconds. 



If it were strictly true, as a very great philosopher 

 and mathematician has advanced, that the velocity with 

 which a hot body, exposed to cool in a cold fluid me- 

 dium, parts with its heat is as the difference of the tem- 

 peratures of the body and of the medium, it is most cer- 

 tain that the curve PQ could be no other than the loga- 

 rithmic curve. Perhaps it may be so in fact, and that 

 the variations from it which my experiments indicated 

 were owing solely to the imperfection of the divisions 

 of our thermometers. If it be so, it is not impossible 

 to divide the scale of a thermometer in such a manner 

 as to indicate with certainty equal increments of heat, as 

 thermometers ought to do ; but this is not the proper 

 place to enlarge on this subject. I may perhaps return 

 to it hereafter. 



Passing over in silence a number of experiments I 

 made in order to get thoroughly acquainted with my 

 new instruments, and to assure myself that the results 

 of similar experiments made with them were uniform 

 and might be depended on, I shall now proceed to give 

 an account of several experiments made with pointed 

 views, the results of some of which were very inter- 

 esting. 



Experiment No. i. The large cylindrical vessel No. i, 

 with its ends covered with warm clothing, in the man- 



