35 i 



GEOLOGY OF THE COMSTOGK LODE. 



due to the normal element E and the lode electromotive force compensat- 

 ing each other in G), approximately, 



e-E-^. 



The resistance r was wrapped on a small piece of wood and the whole sub- 

 sequently boiled in paraffine. The body of the key 

 I K, and that of the commutator C, were similarl}' pre- 

 pared, being boiled in linseed oil, and the merciny 

 cups covered internally with a thick coating of wax. 

 I ^ Moreover, the wires of both in passing through the 

 I wood were additionally insulated from tlie latter by 

 I a covering of gutta-percha; the ends onlj^ being 

 % IT" uncovered and communicating with the mercury in 

 .-? the cups. In consequence of these precautions it 

 •S was found that this comparatively complicated 



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I § method could be employed in these wet drifts with 



S complete success, and the adjustments having once 



"2 been made, it proved to be nearly as expeditious as 



i I either of the other methods. 



"^ As the result obtained is derived from an ex- 



I pression which is independent of the resistance of 



•3 I the circuit, the method could be used with advantage 



I in studying the manner of variation of potential in 



■B passing, as it were, continuously from any T. C. to 



^ I the next. But the actual observations will be more 



■S approjjriately cited in connection with another topic 



'■^ (see page 3G1). 



^' « It will be remembered that in the former ex- 



I periments four contact bags were used throughout, 



which were so combined as to give three indepen- 



- dent values for the electromotive force to be meas- 



s S 2 lu-ed. Tlie results thus obtained, however, being 



° S § 



41 I 7 usually so nearly identical, it was thought that this 



precaution might safely be dispensed witli. Two contact bags only, there- 



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