138 Rev. 0. Fisher on tlw Residual Efect of a Former 



about that of the deep well at Wheeling, W. Va., iu the 

 United States. 



Depth in 



Feet. 



Difference in 

 Degrees Fahr. 



Depth in 

 Feet. 



Difference in 

 Degrees Fahr. 







o-oo 



2640 



7-19 



240 



0-68 



2880 



7-79 



480 



1-35 



3120 



8-37 



720 



2-03 



3460 



8-95 



960 



2-69 



3700 



9-51 



1200 



336 



3940 



10-05 



1440 



402 



4180 



10-58 



1680 



4-67 



4420 



11-10 



192U 



531 



4660 



11-60 



2160 



5-95 



4990 



12-08 



2400 



6-57 







When this curve is plotted it is found to differ not appre- 

 ciably from a straight line, and the mean gradient for the 

 whole depth of 4990 feet will be 1/58*2. From this it appears 

 that the effect of the glaciation will have been to reduce the 

 gradient from 1/51, which it otherwise would have been, to 

 1/58*2 ; but the temperature-curve will not show appreciable 

 alteration from its original form of a straight line. In fact 

 the error at 2400 feet made by taking the temperature-curve 

 as a straight line down to 4990 feet would be o, 76 F. ; and 

 observations could not be relied upon within that limit to 

 base any calculations upon them. In some deep explorations 

 there has been found an increase in the rate in the lower 

 portions. This, we see, cannot be due to a former glaciation ; 

 for that would, if anything, have an opposite effect. It must 

 therefore be attributed to varying conductivity, or to some 

 disturbing cause vitiating the observations. 



The diminution of the mean gradient to a given depth 

 will be greater if the time is less. Thus if, instead of 40,000 

 years, the time had been taken at 30,000 years, the gradient 

 to the same depth of 4990 feet would have been reduced from 

 1/51 to l/59'4. So that the effect of shortening the time from 

 40,000 to 30,000 years will be to reduce the mean gradient 

 between the surface and nearly 5000 feet by about one more 

 degree Fahr. per foot. 



If we consider that the conductivity from stratum to stratum 



