374 Prof. W. E. Ayrton and Mr. W. R. Cooper. 



Tempera. Cure. 



FlG-. 3. — Temperature first falling and then rising. 



for both rising and falling temperature, and that the range is suffi- 

 ciently extensive for the conclusion of the experiment to be unaffected 

 by the lag due to the first slope of temperature. 



But if the lag has a different value for rising and falling tempera- 

 ture, the shape of the curve will be different. Suppose the tempera- 

 ture to be first lowered ; then if the lag is large for a falling and 

 small for a rising temperature, a curve of the form PQ, starting from 

 P, fig. 3, will result, the falling curve PQ (by which we mean the 

 curve for falling temperature) diverging considerably from the 



often employed loosely for the latter, for the sake of brevity in descriptions. 

 Observations with falling temperature are marked on these curves thus — ( x ), and 

 with rising thus — (©) All differences of E.M.F. are expressed in ten-thousandths 

 of a volt and temperature in degrees Centigrade. 



