42 



Mr. C. Chree. 



— A table was formed giving the increase in the galvanometer read- 

 ings for each minnte of each experiment. If there had been much 

 variation in the sensitiveness of the galvanometer, the numbers obtained 

 from each experiment were multiplied by a number varying inversely 

 as the total increase in the readings during the fifteen minutes of that 

 experiment subsequent to the application of the heat. The numbers 

 for each minute were then added together, and the sum gave the 

 mean rate of heating for the minute in question. From these rates 

 the time of fastest heating could be easily calculated, or could be 

 obtained graphically by constructing the curve whose abscissae were 

 the times elapsed since the heating, and whose ordinates were propor- 

 tional to the rates of heating. 



It will be best to consider first the experiments in which the water 

 was siphoned from the dish, as the arithmetic required to obtain the 

 conductivity from the equation (7) is then comparatively simple. It 

 is assumed that the heat passed into the liquid for the first three half- 

 minutes according to the law given in Table I, and that subsequently 

 no heat at all was either given or lost through the dish. As it took 

 some time to perform the siphoning, and there were no doubt slight 

 variations in the small quantity of water left in the dish, the above is 

 only approximately true, but the multiplication of the observations 

 would tend to eliminate the errors. 



If x z pcJ4Jc be denoted by X, then from (7) and Table I, since t = 9, 

 we have for water — 



606(8-75)- 9 /2 e -x/8-75{x2-|X(8-75)+|(875) 2 } 

 + 386(8-25)- 9 / 2 e- x / 8 - 25 {X 2 -|X(8'25) +K8-25) 2 } 

 + 241(7-75)-9/2 e - x /7-75{X2-fX(7'75)+|(7-75) 3 } = 0. 



From this equation X must be obtained by trial. If U stand for 

 the left-hand side of the equation, it will be found that the corre- 

 sponding values of X and U are as follows : — 



X. U. 



22 -88-6 xlO-* 



227 - 8-5 xlO- 3 



22-8 +1 xlO-* 



The value of U is best found by considering the logarithm of the 

 several lines in succession. The following are the values of these 

 lines : — 



X. First line of U. Second line. Third fine. 



22 .... -101-8 xlO- 3 .... -12-7 xlO" 3 .... +25-9 x 10-» 

 22-7. .. - 60-5x10-3 .... +10-21x10-3 .... -+41-77 x 10-* 

 228.... - 55-lxlO" 3 .... +12-05x10-3 .... + 44-05 x KM 



