50 



BULLETIN OF THE NATURAL HISTOKY SOCIETY. 



depth and read only to half a degree ; but it would have 

 been far better, if time had allowed, to have taken them 

 for every foot and for smaller fractions of a degree. In 

 the diagram (Fig. 2) the results are shown graphically, 

 bringing out clearly A, the absolute fall, and B the rate 

 of fall in temperature at the different depths, and C the 

 amount of vertical space occupied by each degree of 

 temperature. The air temperature in the morning over 

 the lake was 71° F. 



Fig. 2. Diagram of temperature in the lake. 



Figures on abscissa (horizontaO =- depths from surface in feet. 



Figures on ordinate (vertical)™ degrees Fahrenheit. 



A-ab.solute drop in temperature. B =rate of drop at the different depths. 

 C amount of vertical space occupied by each degree (approximate), obtained by 

 extension from the points where the curve A crosses the temperature lines. 



(The irregularities in the curves between 39 and t)3 feet are of cours- due to the 

 relative coarseness of the measurements. No doubt very minute measurements 

 would give even curves. In curve B is a slight error in the drawing; on line 30 the 

 point should be lower, and on 33 higher, so curve from 27 to 3ti would be more evenj. 



