4 Mr. E. H. Griffiths and Miss Marshall on the 



ability of the observer to maintain the thermal balance. In 

 these experiments the correction was usually small, and in 

 any case could be determined with great accuracy. 



" Having indicated the nature of the observations, we 

 proceed to state the relation between the various sources of 

 loss or gain of heat. 



" Let Q E be the thermal units per second due to the electrical 

 supply; 

 Q s be the thermal units per second due to the mecha- 

 nical supply ; 

 2# be the total heat-supply during an experiment 

 from any other causes. 

 " Then, if M be the mass of water evaporated, L the latent 

 heat of evaporation at temperature 0, and if the electrical 

 supply is maintained for a time £ E , and the mechanical for a 

 time * gJ 



ML = Q.*.+Q.*. + 20 (1) 



" Now the D.P. at the ends of the coil was always some 

 integral multiple of the D.P. of a Clark cell. 



" Let e be the D.P. of a Clark cell, n the number of cells, 

 and Hi the resistance of the coil at the temperature l9 then 



«.-£ < 2 > 



" If the calorimeter at the commencement and end of an 

 experiment was at exactly the same temperature as the sur- 

 rounding walls, then, if their temperature was unchanged, 

 the term 2<? would vanish ; but although this term through- 

 out these experiments was of small dimensions, it could not 

 be entirely ignored. 



"Let 0q and o ff be the temperature of the surrounding walls 

 at the beginning and end of an experiment ; suppose the 

 calorimeter temperature (0 A ) to exceed the surrounding tem- 

 perature by d' at the commencement and d" at the end of an 

 experiment. Then fall in temperature of calorimeter 



= (0 o ' + d')-(0 o " + d"). 



Hence the heat given out by the calorimeter in consequence 

 of this fall in temperature is 



C ei {W + d')-W + d")h 



where C e is the capacity for heat of calorimeter and contents 

 at the temperature X . 



" If we neglect any small loss by radiation, &c, due to the 



