Variations in the E.M.F. of Clark Cells with Temperature. 375 



normal direction, shown by the dotted line. The rising curve, on the 

 other hand, will be nearly parallel to it. But if the lag is small for 

 a falling and large for a rising temperature, a curve of the form 

 P'Q', fig. 3, will result, the falling curve P'Q' having nearly the 

 normal direction, while the rising curve will diverge to a much 

 greater extent. 



Similar curves will be obtained when the temperature is instead 

 first raised and then lowered. If the lag is larger for falling than 

 for rising temperature, a curve of the form PQ, fig. 4, will result, 

 wider near the starting point P than at the other end, whereas if the 

 converse is the case the curve will be of the form P'Q', narrower 

 near the starting point than at higher temperatures. 



Temperature. 



P 



Fig. 4. — Temperature first rising and then falling. 



Any lag of the ordinary kind will soon pass off after a steady tern- 

 perature is reached, or after the temperature gradient is reversed. 

 But any lag of a semi-permanent character will prevent the curve 

 from returning to its starting point until after the lapse of a con- 

 siderable time, and will thus produce a break. 



