M. Scheerer ow the Products of Oxidized Pyrites. 265 



in the adjoining conductor ; since this tends to produce a 

 current in the opposite direction. 



96. It would also appear from the perfect neutralization 

 which ensues in the arrangement of the last paragraph, that 

 the induced current in the adjoining conductor is more power- 

 ful than that of the first conductor; and we can easily see 

 how this may be. The two ends of the second coil are joined, 

 and it thus forms a perfect metallic circuit; while the circuit 

 of the other coil may be considered as partially interrupted, 

 since to render the spark visible the electricity must be pro- 

 jected, as it were, through a small distance of air. 



97. We would also infer that two contiguous secondary 

 curi'ents, produced by the same induction, would partially 

 counteract each other. Moving in the same direction, they 

 would each tend to induce a current in the other of an op- 

 posite direction. This is illustrated by the following ex- 

 periment: helix No. 1 and 2 were placed together, but not 

 united, above coil No. ], so that they each might receive the 

 induction ; the larger was then gradually removed to a greater 

 distance from the coil, until the intensity of the shock from 

 each was about the same. When the ends of the two were 

 united, so that the shock would pass through the body from 

 the two together, the effect was apparently less than with one 

 helix alone. The result, however, was not as satisfactory as 

 in the case of the other experiments ; a slight difference in 

 the intensity of two shocks could not be appreciated with 

 perfect certainty. 



[To be continued.] 



XLVII. On the Natural Products *which originate from the ac- 

 tion qftheJtmosphere on Iroyi Pyrites. By Th. »Scheerer*'. 



TT is a well-known fact, that iron pyrites,in the finely divided 

 -*- state in which it occurs in alum slates, is easily oxidized by 

 the atmosphere, causing the parts exposed to acquire a reddish 

 brown colour ; nevertheless, the products of this decomposi- 

 tion are seldom to be found, from the rain washing them away. 

 In a spot near Modum in Norway, I met with a cavity in the 

 mountains where they were deposited as incrustations, safe 

 from all destructive influences. Three distinct layers were 

 evident. 



The first and upper layer is a dark brown massive mineral 

 with which the slate is impregnated : A. 



* An extract obligingly comniunicated by the author from the original 

 paper published in PoggendorfF's Annalen, vol, xlv. p. 188. 



