18 REPORT — 1841. 



II. On the second hypothesis A = 199-57 and log e~^ = — '08278, and 

 the following are the results : 



4-5678 9 10 11 12 13 14 



80-5 65-34. 53-32 43-6 35-72 24-07 16-3 11-06 7-52 5*12 3-49 



III. M. Poisson's method, when the value of e~^ deduced from the pre- 

 ceding hypothesis is retained, gives y — 2m =: -0031825 ; and we have 



4 5 6 7 8 9 10 11 12 13 14 



80-5 65-55 53-5 43-75 35-84 24-15 16-35 11-09 7-54 5-15 3-5 



IV. The fourth hypothesis gives 



4 5 6 7 8 9 10 11 12 13 14 



84-9 67 53-75 43-51 35-5 24. 16-45 11-39 7-9 5-5 3-8 



The next series of experiments similar to the above we obtain from the 

 work of M. Despretz, entitled ' Traite de Physique.' The author read be- 

 fore the Academy of Sciences in 1821 a memoir, the object of which is to 

 measure in a number of substances the conductive power relative to heat. It 

 is published in the ' Memoires des S^avans Etrangers.' An account of it ap- 

 pears in the ' Annales de Chimie,' t. xix. (1821) p. 97, by M. Fourier, and it 

 is extracted in works referred to above (1825). We have added the exa- 

 mination of the four formulae by means of these experiments. We shall find 

 that they all come very wide of the results, even in cases differing in no ap- 

 parent particular from those given by M. Biot. This is remarkable, for all 

 the formulas agree well with M. Biot's experiments. To what circumstance 

 can we attribute this fact ? It cannot be supposed that the presence of the 

 air should vitiate one series of experiments without affecting the other, in 

 which everything else is similar. We can only suggest, that the bars whose 

 conducting powers were examined, were not sufficiently long to be regarded 

 as infinite. Unfortunately M. Despretz does not mention their length. The 

 experiments were as follows : 



(4.) The stationary excesses of temperature above that of the air, at dif- 

 ferent points of a bar of copper taken at equal distances from each other, 

 were found to be as follows : . 



No.ofther.... 12 3 4 5. 6 



Exc.oftemp. 66-36 46-28 32-62 24-32 18-63 16-18 

 The temperature of the air was 17-08°, and the distance between tAVO con- 

 secutive thermometers ten centimetres. 



The following are the calculated results, by the four hypotheses respect- 

 ively, using in each case the results of the first and third thermometers for 

 the determination of the constants. 



I. 1 2 3 4 5 6 

 66-36 46-45 32-62 22-83 15-98 11-19 



II. Here e~^-714 and A = 61-54. 



1 2 3 4 5 6 



66-36 46-45 32-62 22-83 15-98 11-19 



III. e~^is assumed to be equal to -714, and y — 2 w is determined to be 

 .003271. 



12 3 4 5 6 



66-36 46-28 32-62 23 16-3 11-47 



IV. 1 2 3 4 5 6 

 66-36 46 32-62 23-5 17-1 12-5 



(5.) A bar of iron circumstanced as the preceding. The temperature of the 

 air was 17-34°. 



No. of therm.... 12 3 4 5 6 



Excoftemp.... 62*9 36-69 20*52 12-32 8-19 6-61 



