ELECTRICAL ACTIVITY OF ORK BODIES. 



119 



Table II. — Experiments in the Con, Virginia and California^ 175Q-foot lereL 



[Gads (Iriveu into rock, as free from mineral matter as possible, about 8 feet apart.] 



The results are highly in favor of wet gads. By their use a very 

 marked diminution of resistance is effected without increasing- the values of 

 e. The direction in which s acts follows no observable law, probably being- 

 conditioned by the electrical difference of the gads and by effects of pohir- 

 ization due to the introduction of a Daniell. 



Analogous experiments were also made with copper and zinc. These 

 metals were used in the form of strips cut from sheets. Each strip was 

 bent around the small end of a sliglitly conical stick of wood about one 

 foot in length. The plug was then firmly driven into a hole previou.sly 

 drilled for the purpose, in such a way as to force the metal into thorough 

 contact with the rock Table III. gives the results, the notation being the 

 same as that used in Table I. 



Table III. — Experiments in the Con. Virfjinia ami California, 17 50-foot level. 



[Plugs about 10 feet apart in moist cl.ay seams, repeatedly exclianged as indicated.] 



