TfiMPKRATURE-MEASl'RE^IICXTS IX CIJCAK LAKE. 51 



In synopsis the results are as follows : 



1. For the first 12 feet there is no appreciable fall in 

 temperature : from 12 to 18 feet there is a slight fall, l^*^; 

 at 18 feet a very abrupt fall begins and continues nearly 

 evenly to 80 feet, and in these 12 feet it drops no less than 

 17tV% or about IJ*^ per foot; below 80 feet the rate ot 

 fall diminishes until the minimum 42i''' is reached at 

 about (JO feet. 



The meaning of these figures is no doubt this : that 

 down to 12 feet the effect of the sun's light and heat is 

 strongly and evenly felt, and the surface movements help 

 to distribute it ; after about 12 feet the heat has been 

 largely absorbed, while at 18 it has been almost entirely 

 taken up ; the layers below that probably derive their 

 temperature by conduction from those above them. 



2. There are faint indications in the table that at 

 depths beloAV 30 feet the temperature near the bottom in 

 the shallower places is slightly higher than at the same 

 depths over dee})er places, indicating that the ground 

 slightly warms the water in contact with it, which is to 

 be expected since it is a better conductor than water. 

 But so slight are these indications that they ma}' be 

 neglected and it may be said, at least of the greater 

 depths, that their temperature is a function of (Ustance from 

 the surface and bears no relation to the bottom. 



3. The results give no positive information about 

 the presence of springs. 



It would have been of great interest had I been able 

 later in the summer to make a second series to determine 

 whether the average temperature of the lake was raised 

 throughout, but this was not possible. I have not been 

 able to compare the results obtained by others elsewhere, 

 though with other instruments the subject has been much 

 studied in Europe, and to some extent in Anierica. 



