64 Mr. E. H. Griffiths on the Influence of 



temperature difference equivalent to 1 centim. of the bridge- 

 wire, but would of course have the same relative values in 

 any scale. 



p = -000082. 



( 



a = -000230. 

 §0=-O1467O. 



Let us assume that the value taken for N differed from 

 the true value by as much as 1 bridge-wire degree (as will 

 be seen when the experimental results are given this is an 

 excessive estimate), then l — N = 1, hence (supra) the value 



<lf) 

 of ~r- ■ would differ from 

 at 



^ by M^) = -000082X1 = . 00009. 



dt J n 1 9 



JQ 1 



When the values of -i^— i (where n = 2, 3, or 4) were 



plotted as ordinates with l as abscissa, the resulting straight 

 lines were found to intersect not in one but in three points, 

 which, however, were so near to each other that (except in 

 one case) the probable error introduced by assuming that any 

 one intersection gave the true value of 6$ was less than that 

 above indicated. The triangle formed by joining the three 

 points of intersection was almost invariably of one form and 

 of nearly equal dimensions, indicating that its existence was 

 not due to experimental irregularities but was connected in 

 some way with the difference in the rate of rise with different 

 values of n. I think that my impression that p and hence 



fl-v are functions of — - is thus confirmed. 

 N at 



In any case the error caused by the assumption that 0$ is 

 the same with different rates of increase in temperature, must 

 be less than the error resulting from the assumption that it is 

 the same when the temperature is rising and when it is 

 steady. 



Again, the null point finally selected for each group of ex- 

 periments was always obtained in the same manner from the 

 three points of intersection. Any error, therefore, is of the 

 same nature in each case, and as the specific heat was obtained 

 by the subtraction of one ordinate from another, the effect of 

 any error is diminished considerably. True, when the absolute 

 value of the ordinate is used in order to obtain the water 

 equivalent of the calorimeter, any error in the position of 6^. 



