168 M. Becquerel on the Electric Origin of 



that, if it were otherwise, the appearances of decomposition in 

 the same localities would be much more marked and general 

 than they are found to be. He ^marks also, that when copper 

 pyrites and vitreous copper-ore form a voltaic combination with 

 pure or spring water, there are considerable electro-magnetic 

 effects. We would merely observe, that Mr Fox appears not 

 to be aware, that the electro-chemical effects produced in the 

 contact of two solid bodies and a liquid, depend solely on the 

 chemical relations of their constituent parts, and must fre- 

 quently vary. 



Let us now approach the researches of the same gentleman 

 on the electro-magnetic properties of the metalliferous veins of 

 Cornwall, in which he has been engaged for six years past. 



The apparatus which he has used in examining these pro- 

 perties is composed of small plates of copper, fixed on the por- 

 tions of the veins submitted to experiment with iron nails,* or 

 strongly pressed by means of wooden supports, and put in con- 

 nexion with the extremities of a multiplier, of which the wire 

 is short, and the directive power of the needle not neutralized. 

 Mr Fox says, that with this apparatus he perceived the fol- 

 lowing effects : — The intensity of the current varies, according 

 to the localities. Sometimes the deviation of the magnetized 

 needle is slight, sometimes it is considerable. In general, it is 

 greater when the vein contains a larger quantity of copper, and 

 perhaps even from the depth of the stations. He adds, that 

 there is no, or scarcely any, action perceptible where there is 

 little or no metaUic substance. When there is a distance of but 

 a few fathoms between the plates in a horizontal direction, and 

 when there is between them a great quantity of copper not in- 

 terrupted by non-conducting substances, there is no action ; but 

 if there be, by chance, quartz or clay in the vein, the action is 

 generally very decided. 



When the two plates are placed at various depths in the 

 same^vein, or in different veins, the electrical action is in gene- 

 ral very marked. The currents are sometimes in one direction, 

 sometimes in another. In comparing parallel veins, he thinks 



• Nails were very seldom used, and those that were were always of copper, 

 W. J. H. 



