170 M. Becquerel on the Electric Origin of 



that the veins on which the mines are worked traverse both the 

 granite and the micaceous rocks (slates) ; that they are princi- 

 pally composed of quartz and other earthy minerals, mixed in 

 many places with copper pyrites, iron pyrites, vitreous copper- 

 ore, oxide of tin, blende, and galena, and occasionally with na- 

 tive copper, protoxide and the carbonates of the same metal^ 

 and of some of the salts of lead, in small quantities. 



At the greatest depths, the temperature of the slate-rocks is 

 two or three degrees higher than that of the granite at the same 

 level. 



In many of the deepest mines, the water contains salts in va- 

 rious proportions. Among others, the chlorides of calcium, of 

 sodium, and of magnesium, &c. 



Mr Henwood has adopted the mode of experiment already 

 described. The metallic plates were placed at distances vary- 

 ing from a few feet to many hundred feet, at the same, and at 

 different levels. 



The results have been the same whatever the directions of 

 the veins might be. In those which only produced tin, and in 

 many where they were in contact with copper, no traces of a 

 current were perceived, except in some cases where the inter- 

 mediate space was filled with rich copper-ore.* The presence 

 of electricity was more evident when the vein contained copper- 

 pyrites, vitreous and black copper-ore, galena, or blende. It 

 was not detected when the vein was entirely without metal. 

 Some veins which contained copper-pyrites, grey copper-ore, 

 and galena, and others with carbonate and phosphate of lead, 

 and grey copper-ore, gave no evidence of the existence of cur- 

 rents. 



It appears that Messrs Fox and Henwood have not remarked 

 the relations which subsist between the directions of the veins 

 and those of the currents.f 



In the experiments where they have connected metalliferous 



• " In most cases where there was a continuous mass of copper-ore between 

 the points examined, no electricity was detected. In some instances, how- 

 ever, where all the intervening space consisted of rich copper-ore, there was 

 most energetic action." — Edin. New Phil. Journal^ xxii. p. 274. 



t There must be some misprint or misapprehension here, as the directions 

 of the veins have been mentioned in paragraph preceding W. J. H. 



