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DEPTH 3CALE FOR MICHK3AN 3, ODD 



FiGUKB 1. — Diffeienvea from deepest a-ra4ient ire Jfl«ftj(;o>i 



Probability curve In left corner. 



Figure 1 shows by the heavy black area In the lower left corner the probability curve 

 (1 — Pm), unity for m being Indicated hy a distance. The same distance from left to 

 right as the depth of 1,000 feet, and in ordinates 10 degrees Fahrenheit, and the circles 

 indicate the number of degrees by which the actual rocit temperatures observed at depths 

 corresponding to the abscissas are In excess of those which might be expected from the 

 temperatures and the gradient at the bottom of the mine. 



FiGDEE 2. — Temperatures in Michigan 



Figure 2 shows to the same depth scale, running from left to right, the temperatures 

 (referred to the scale on the left) for various depths In Michigan copper mines, by 

 hollow circles with a radius equivalent to one degree. Half circles Indicate a greater 

 range of probable temperature. The heavy black line Indicates the bottom gradient, 

 one degree Fahrenheit in 90 feet 



Figure 3. — Temijeraturea in Lake Well, West Virginia 



Figure S shows by solid black circles with a temperature scale to the right and a 

 depth scale below, \^1th the units in each half the size of those in Figure 2, so that tlie 

 slopes are directly comparable, the temperatures and the bottom gradient as measured 

 by C. H. Van Orstrand at Lake, West Virginia. 



