AS AFFECTING SPRINGS. 131 



Bischof recommends us to examine, if possible, 

 once or twice a month during a year, the tem- 

 perature of more than one spring in the same 

 neighbourhood \ adding that the annual mean of 

 the coldest will approximate closely to the true 

 mean temperature of the ground in the locality. 



Shallow wells which are in constant use, being 

 fed by the land-springs filtered from the surface 

 soil, or deriving their supplies from neighbouring 

 rivers or brooks, have a temperature varying with 

 the seasons, or even from week to week, so that 

 their annual mean cannot differ very far from that 

 of the ground. 



k 2 



