396 OBSERVATIONS AND EXPERIMENTS 



points of the spark-micrometer were put in the latter circuit, two 

 sparks, one larger, immediately followed by a smaller, were seen to 

 pass regularly between the points. As these experiments were still 

 made without the frog-interrupter, it is possible that the two sparks 

 may have proceeded from two different shocks, bat the regularity of 

 their appearance leads me to believe that they belonged to the begin- 

 ning and ending current, which corresponded with the rise and fall of 

 one and the same shock. But it is interesting and important, that 

 in accordance with the above principle, we can in this manner 

 obtain from the fish a current which passes over a erap between 



.t O -IT 



fixed metals. That this principle actually prevails here, seems 

 to follow from the circumstance, that the sparks failed to pass when 

 the lengths of wire of the primary coil were connected, so as to have 

 double length and half thickness. 



5. Magnetisation. 



The effect of the introduction of the wires in the coil used 

 for obtaining the passage of the spark is to be attributed to the 

 electro-magnetisation of soft iron. 



Six completely unmagnetised sewing needles 37 mm. long, 0-7 

 mm. thick, separated from each other by wax, were put in the 

 hollow axis, 8 mm. wide, of a coil which consisted of 735 turns of a 

 copper wire, 0-4 mm. thick. Three shocks of Malapterurus sufficed 

 to magnetise the needles decidedly strongly, though not to 

 saturation. Ten single opening shocks of the ordinary induction 

 apparatus (one Grove, with the coil quite pushed up) did not make 

 the needles perceptibly magnetic ; this was only accomplished when 

 the spark-current had passed for some time through the coil. This 

 current was, however, somewhat more effectual than the shock of 

 the fish. 



6. Electrical Attraction. 



The surest indication of electricity has always been its longest 

 known effect electroscopic attraction and repulsion. I pass over my 

 unavailing experiments, which were however not long continued, to 

 charge a Leyden jar or a condenser by the fish. Since then, this 

 task has been very perfectly accomplished by Armand Moreau 

 with the Torpedo 1 . But I frequently observed the electrical 

 attraction of two gold leaves by the electricities of the shock 



1 Comptes rendus, etc., 1862, vol. liv. p. 963 : Annales des Sciences naturelles, 4*" 

 Serie, Zoologie, 1862, vol. xviii. p. u. 



