March i6, 1893] 



NATURE 



477 



its bearings were outside the steel chamber, and that the 

 water was thrown from the bottom to the lid of the calori- 

 meter. 



More than lOO experiments were performed (many of them 

 lasting several hours) in order to determine the value of 

 (T + p (fij - ff„\/ when the calorimeter contained different masses 

 of water. The harm my amongst the results was satisfactory. 



The pressure in the space between the calorimeter and the 

 walls of the steel chamber was reduced, as a rule, to between 0-3 

 and romm.- 



The absolute value of the loss by radiation, &c., at different 

 pressures was ascertained, and it was found that the rate of gain 

 or loss decreased very rapidly when the pressure was reduced 

 below o "5 mm. 



If I M is the rate of rise due to the non-electrical supply, 



and j ? J that due to the electrical supply, 

 then 



5ii = f««l\ + / WA (I) 



We have indicated the manner in which we determined the 

 last term of this equation, and thus, by direct observation of 



^ we were able to obtain the value of ( .' I and 



\S/J. J.R'.M' 



(2) 



where R' is the resistance of the coil, and M' the capacity for 

 heat of the calorimeter and its contents at a temperature flj 



Throughout the experiments E was kept constant, the 

 arrangement for maintaining the ends of the coil at a con- 

 stant potential difference worked admirably, and it is probable 

 that in no case did the variations exceed 1/10,000 of the mean 

 potential difference during each experiment. 



'l"he value of R was determined by a direct comparison (con- 

 ducted by Mr. Glazebrook) with the B. A, standards and 

 values of R were expressed in true ohms as defined in the B. A. 

 Report, 1892. 



The difference between the temperature of the coil and that 

 of the surrounding water was ascertained, and the resulting 

 difference of resistance was found to be such that5R= •oo422«''^, 

 where « was the number of Clark cells by which the potential 

 difference at the end of the coil was maintained. 



The mercury thermometers were standardised by direct com- 

 parison with several platinum thermometeis, and a further com- 

 parison has (through the kindness of Dr. Guillaume) been 

 made with the Paris hydrogen standard. The difference ob- 

 tained by the two methods in the value of the range is only 

 •005° C. 



The various quantities in equation (2) having been determined 

 (with the exception of J and M'), we •an deduce from equation 

 (2) the time (T) of rising 1° C at any point of our range when 

 R = loiandE is the potential difference of one Clark cell at 



15= C. 



We thus get 



(3) 



If w be the weight of water, and Wx the water equivalent of 

 the calorimeter at the standard temperature, and if / and ^ be 

 the temperature coefficients of their specific heats, then 



hence 



M' 



J ': 



E-" 



= -v{i +/&i - e) 4- Wxil +gBj - e); 



lii +/0r^e) + w,[i+ ^T^^e); = T . . (4) 



By repeating observations with different weights of water, w^ 

 and Tfj, and observing Tj and Tj, the corresponding times, we 

 obtain by subtraction 



i(«'2 - w,) (I -t- A~e) - T, - T3 . . . (5) 



Hence when 0, = 9 {i.e. at the standard temperature) we can 

 find J without first ascertaining the values of/, g, or the water 

 equivalent of the calorimeter, and by repeating the observations 



1 «r = rise in temperature per i second due to the stirring, p = gain 

 or loss in temperature per i second due to radiation, &c., when 01-9,,= 



i°c; 



2 The pressures were ascertained by a McLeod's gauge. 



over different ranges we can find /withoat previously obtaining J; 

 or, having obtained/, we can find Wj and^, and then by equa- 

 tion (4) deduce the value of J from a single experiment. We 

 have adopted both methods as a check upon the calculations, 

 which involve much arithmetic. The latter method is the more 

 convenient, as it enables us to ascertain the results of separate 

 experiments, but it cannot be applied until the values of /, g, 

 and Wx have previously been obtained by observations on two 

 different weights at two different temperatures. 

 We give the values of T at 15°, 20 , and 25° C. 



Tablk XLI.— Values of T at 15°, 20°, and 25° C. 



Fr9m this table we obtain the following results : — 

 Specific heat of water at 25° in terms 

 of water at 15°, deduced from columns 



4 and 6 = 0-99734 



Ditto from columns 4 and 5 . . . . = 0-99722 

 Ditto from columns 5 and 6 . . . . = 0*99746 



Mean = 0-99734 



Hence, adopting 15° C. as the standard temperature, the 

 Specific Heat of Water = l-0"000266 (^-15).^ 

 Also by means of equation (15) we get the following value* 

 ofj:- 



Columns 4 and 6 J = 4-1939 x 10^ 



4 M 5 J = 4-1940 X 10" 



„ 5 » 6 J = 4-1940 X io7 



Mean 



J = 4-1940 X 10' 



This value of J, as previously pointed out (equation 5), is 

 entirely independent of the value assigned to the water equivalent 

 of the calorimeter. 



And we find the water equivalent of the calorimeter at 15° C. 

 in terms of water at 15° C. = 85-340 grams. The water equi- 

 valent of the calorimeter at 25" C. in terms of water at 15° C. 

 = 86-174 grams. 



Hence water equivalent = 85-340(1 + o-ooo977(/ - I5)|. 



We can now find the capacity for heat of the calorimeter and 

 contents for any weight of water at 15 , 20°, and 25° C, 

 and deduce the value of J from each group separately. 



Table XLIII. — Values of J. 



We have in the above table given the values resulting from 

 the calculation at different temperatures, for the limit of our 

 experimental errors is thus clearly indicated, since the values of 



J Over the range 14° to a6° C. 



NO. 



1220. VOL. 47] 



