244 GEOLOGY OF THE COMSTOCK LODE. 



Section II. 

 THERMAL SURVEY. 



Temperature observations. — Valuable tempcraturG obsGrvations have been taken 

 on four lines near the Comstock, viz., in the Cornhination, new Yellow Jacket, 

 and the Forman shafts, and in the Sutro Tunnel. These observations were 

 all made at freshly exposed points as the excavations progressed, at a dis- 

 tance from all other workings, and while not unaffected by some of the dis- 

 turbing causes mentioned on page 229, form a far more trustworthy guide as 

 to the theoretical conditions of the Lode than a similar number of determi- 

 nations made in the mines. Each set, too, was observed as a matter of 

 routine duty, so that successive observations must have been affected by 

 nearly constant errors; and though many of them were made with less pre- 

 caution than a physicist would have employed, their great number goes far 

 toward compensating for any roughness in the method. Whoever is familiar 

 with the tone of speculative excitement which prevails in the mining regions 

 of the far West, a tone but little in harmony with scientific research, will 

 agree with me that great credit is due to the officers of the mines for 

 making and preserving these records. It would be well for the advance- 

 ment of pure and applied science if such a spirit were general among those 

 whose occupations bring them in contact with natural phenomena. 



Computation of the observ.- -.ions. — The following taWes aud diagrams need but 

 little explanation. On plotting the temperatures taken in the shafts, no 

 indication of curvature could be perceived, and a straight line was therefore 

 assumed as expressing the relation of temperature to depth. 



The equation of this line is 



tzza -\- hd; 



where t is the temperature in degrees Fahrenheit corresponding to the depth 

 d in feet, and a and h are constants to be calculated. The computations by 



