14 Pi'ofessor Reich on the Electrical Cttrrenfs 



but xevj rarely ; only when galena is, with certainty, connected 

 ^vith a point consisting of iron and arsenical pyrites, which 

 occurred in four cases, the current in the wire went always 

 from pyrites towards galena, in accordance with the above 

 series. 



We must not, however, pass in silence a result not very fa- 

 vourable to this hypothesis. When, namely, a non-metalli- 

 ferous point with one of ore occasions a current, Ave should 

 look for the cause in the heterogeneity of the copper disc and 

 the metallic components of the ore ; as now, from the above, 

 all ores are negative referred to copper, the current should go 

 in every case towards the non-metalliferous point. We have 

 seen, however, that of eleven cases this took place only in five, 

 whilst in six cases it was in the opposite direction, — were 

 there, perhaps, ores in the vicinity of the non-metalliferous 

 point, whose intensity exceeded that of galena and copper ? 



VII. With regard to the extent of the deviation of the mul- 

 tiplicator, it is to be borne in mind, that there can be no im- 

 mediate conclusion drawn from this as to the electric difference 

 of the substance coming into play, for this depends on the re- 

 sistance to conduction in the entire chain, which again depends 

 on the dimensions and nature of the intervening rock, as also 

 on the more or less perfect contact between the copper disc 

 and the ore, and between the disc and the wire. It is true, 

 as above mentioned, that, from the connection of almost ex- 

 actly the same two points, I obtained on one occasion 32°, 

 on another 72° of deviation. The cause of this lay probably 

 only in the fact that, in the first case, the Avire was attached 

 by merely turning up a corner of the copper disc upon it, 

 while in the other case it was pressed to the disc by a clamp 

 or vice made for the purpose. An idea of how small the 

 power of the electrometei's hei'e in action is, may be derived 

 in some measure from the observation, that a zinc-copper ele- 

 ment introduced, Avhose current went in the opposite direction 

 to that observed, surpassed in effect the latter in every case. 

 If the deviation of the needle was great, it was so also on ap- 

 plication of the zinc-copper element to the opposite side, — if 

 the deviation was small, then so was that occasioned by the 



