184 Mr. W. R. Grove on Magneto-Electric Induction. 



The results tabulated give the following percentage compo- 

 sition : — 



I. II. 



Arsenic 34*45 35*84 



Sulphur 20-01 1975 



Nickel 21-59 23-16 



Cobalt 6-32 6'64 



Iron 13-12 11*02 



Manganese .... 0*33 0-33 



Copper trace traces 



Magnesia .... 0*66 0*66 



Insoluble silica, &c. . 2-71 2-60 



99-19 100-00 



The analyses on record of this mineral species from different 

 localities vary greatly in percentage composition, although they 

 are all considered to come under the general formula Ni (S As) 2 . 

 The above analysis does not differ more from those generally cited 

 than they do from one another, the only remarkable features being 

 that the percentage of arsenic is somewhat lower than usual. 



In composition it appears to resemble somewhat the crystal- 

 lized specimens from Schladming in Styria, which also contain 

 considerably less arsenic than the formula would require. 



XXI. An Experiment in Magneto -Electric Induction. 

 By W. R. Grove, F.R.S. Z$c .* 



SHORTLY after the publication of Mr. Wilde's experiments 

 on magneto-electric induction, it occurred to me that some 

 of the ordinary effects of the Ruhmkorff-coil might be produced 

 by applying to it a magneto-electric machine. I tried an ordi- 

 nary medical machine with a small coil made by Mr. Apps, of 

 3^ inches length by 2 inches diameter, and having about f of a 

 mile of fine secondary wire. 



The result was very unexpected. The terminals of the mag- 

 neto-electric coils being connected with the primary coil of the 

 Huhmkorff, and the contact-breaker being kept closed so as to 

 make a completed circuit of the primary wire (a condition which 

 would have appeared a priori essential to success), no effect was 

 produced ; while if the circuit was interrupted by keeping the 

 contact-breaker open, sparks of 0*3 of an inch passed between 

 the terminals of the secondary coil of the Ruhmkorff, and vacuum- 

 tubes were readily illuminated. Here there was in effect no pri- 



* Communicated by the Author. 



