Glacial Epoch upon Underground Temperature. 137 



at successive intervals of 80 feet, and we can tabulate the 

 values of 



X 



2b C *Ji7t , 7 



vVJo 



for these depths. 



Now it is easily seen that, if on a diagram we draw the 



straight line -r 7 



& V = mx, 



taking x vertically downwards and V horizontal, it will give 

 the curve of temperature, just before the ice melted, as a 

 straight line. 



Then V=ma; + b will represent a second straight line, at 

 a distance b, parallel to the first; and if we shorten the 

 ordinates of this line by the difference 



2b 



TV 



J." 



-*d/h 



taking L successively = 0*01, 0"02, &c, we get on our diagram 

 successive points of the temperature-curve at the present time, 

 at successive depths of 80, 160, &c. feet, on the supposition 

 that glacial conditions passed away 40,000 years ago. 

 The following table gives the values of the difference 



2b 



f- 



dfi 



at intervals of 80 feet, down to 1120 feet. 



Depth in 



Feet. 



Difference in 



Degrees Fahr. 



Depth in 

 Feet. 



Difference in 

 Degrees Fahr. 







000 



640 



1-80 



80 



0-23 



720 



203 



160 



0-45 



800 



225 



240 



068 



880 



2-47 



320 



0-90 



960 



2-69 



400 



113 



1040 



292 



480 



1-35 



1120 



314 



560 



1-58 



1200 



336. 



And the next table gives the same difference at longer 

 intervals of 240 feet, to the depth of 4990 feet, which is 



