INCREASE OF TEMPERATURE WITH DEPTH. 



265 



THERMAL SURVEYS ON THE COMSTOCK. 



During his study of the Comstock Dr. G. F. Becker made careful thermal 

 surveys along deep vertical shafts and along the Sutro tunnel, which runs in 

 and taps the vein. On plotting the temperatures taken in the shafts no indication 

 of curvature could be perceived, although the increment showed constant local 

 irregularities, and the line, plotted from point to point, was often zigzag. On 

 this account a straight line was assumed as expressing the relation of temperature 

 depth. The Sutro tunnel line, however, though also irregular in detail, shows an 

 unmistakable curve, clearly a conduction curve. It is to be noted, on the other 

 hand, that in the Sutro tunnel the temperature measures extended over a distance 



20 



30 



Degrees Fahrenheit 

 40 50 



60 



80 



90 



Feet 



100 

 200 



300 

 400 

 500 

 600 

 700 

 SOO 

 900 

 1000 



Ohio Tonopah 



Mizpah Extension 



FIG. 77. Plotting of temperature observations in the Ohio Tonopah, Mizpah Extension, and Montana Tonopah mines, 

 showing increase of temperature with depth. a=This part of the curve coincides with that of the Montana Tonopah. 



of 11,000 feet, while the vertical shaft measurement did not extend more than 

 2,000 feet; and that any given 2,000 feet of the Sutro tunnel curve would not 

 by itself suggest a curved line. 



COMPARISON OF COMSTOCK AND TONOPAH DATA. 



Comparing the Tonopah and Comstock data, the temperature of 78 F., 

 obtained in the Ohio Tonopah at 766 feet from the surface, was encountered in the 

 Forman shaft at the Comstock at about 900 feet; while the bottom temperature of 

 73.5 F. in the Mizpah Extension at 780 feet was encountered in the Forman at 

 between 600 and 700 feet. It seems likely, therefore, that the average increase at 



