HEAT OF EVAPORATION OF WATER. 339 
1 millim. of No. Il. = 5°51 millims. of bridge-wire, and 882°40 millims. = 40°:142. 
Bridge-wire null-point = 599°55 millims. 




| Change Correction to| Co™rection for | 
Time A oe Al Resulting temperature | Corrected | 
Range. over | omPerature change d@,/dt x 104. eet C. cells and de,/dé | 
on therm. | bridge-wire. . : Li 
| range. Ir | range. 104. bridge-wire X10 s| 
| ; x 104 | 
centims. | 
| 30 to 60 | 652-9 +°03 +16 | =1533°9 +13 +'4, +11 1536°7 
| 60 to 70 | 695°3 0 0 1438°1 —6-4 +°3, +10 1433-0 






Hence we get ‘15367 and ‘14330 as the values of (d60,/dt)., at 55 and 65 centims. 
respectively. We can thus deduce the value at the null-point (599°55). We get 
"14853. 
Now (Appendix I.) the value of (d6,/dt), for rate 5°277 = °00158, therefore 
(d0,/dt),, = 14695. 
16, \ OF 6 ‘ hs : 2 : 
Now a) « a a gives the rise per second in degrees C. with unit resistance 
/ 3e née )~ 
and unit potential difference, where R, is the resistance in true ohms of the coil at 
temperature 6,, n the number of Clark cells of P.D. e volts, and C; the value of the 
mean bridge-wire millim. at 15° C. when 0, = 40°11, expressed in terms of the N 
thermometer (see p. 289). Hence if T is the time of rising 1° C., we get 

a (ne)? 
7 GOildi), x RYXiC; 
and 
R;, = 10°377 (see Table VIII.), (ne)? = 18°513, and C, = 009100, 
therefore 
i — wo 4ale 
and 
= ; (where C,, is capacity for heat at 0,), and J = 4199, 
therefore 
C,, = 317'82 thermal grams. 
The following table gives the results of all the experiments made with the object of 
obtaining the values of C,. 
