1902 - 3 .] Determining Latent Heat of Evaporation. 459 
with Regnault’s result. Taking this as 536 ’3 (calories at 15°) and 
Joule’s equivalent J = 4*187 (calorie at 15°, Griffiths, Thermal 
Measurement , p. 108), this gives the latent heat in joules per gm. 
= 536*3 x4*187 = 2245*5. Compared with this, the numbers 
2249, 2264, 2266 have been obtained in the order given. These 
numbers seem to indicate a value somewhat higher than Regnault’s, 
but they were obtained with forms of apparatus which subsequent 
experience showed to be unsatisfactory in several respects. It is 
hoped that with the present form more concordant results may be 
obtained. Experiments for this purpose are being continued. 
The apparatus has been made and used in the workshops and 
laboratory of the electrical department of the Heriot-Watt College, 
and I gladly avail myself of this opportunity of expressing to 
Professor Baily my thanks for the facilities he has afforded for 
the work during the spare time of the last two summer vacations. 
( Issued separately August 8 , 1903 .) 
