500 Mr. Grove on the Electro-chemical Polarity of Gases. 



wire its apex ; the wire rapidly fused, and became so brilliant 

 that the cone of flame could be no longer perceived, and the 

 globule of fused platinum was apparently suspended in air and 

 hanging from the mre; it appeared sustained by a repulsive 

 action, like a cork ball on a jet d'eau, and threw out scintilla- 

 tions in a direction away from the water. The surface of the 

 water at the base of the cone was depressed, and divided into 

 little concave cups, which were in a continual agitation. When 

 the conditions were reversed and the negative Avire immersed, 

 the positive wire being at the surface, similar phrenomena ensued, 

 but not nearly in so marked a manner ; the cone was smaller, 

 and its 1)ase much more narrow in proportion to its height. 



This experiment, the beautiful effect of which requires to be 

 seen to be appreciated, indicates a new mode of transmission of 

 . electricity partaking of the electrolytic and disruptive discharges. 

 Not possessing a battery of this enormous intensity, I have not 

 been able to examine this ph?enomenon more in detail ; but I 

 have from time to time made many other experiments on the 

 voltaic arc taken in various gaseous media, with the view of 

 ascertaining the state of the intervening media anterior to, 

 during, and after the discharge ; these experiments have hitherto 

 given me no results of any value. In the voltaic arc, the intense 

 heat developed so affects the terminals and so masks the proper 

 electrical effect, that the difficulty of isolating the latter is ex- 

 treme; and I have latterly sought for some modified form of 

 electric discharge which should be intermediate between the vol- 

 taic arc and the ordinary Franklinic discharge, or that from the 

 prime conductor of a frictional machine ; for something, in short, 

 which should yield greater quantitative efl'ects than the electrical 

 machine, but not dissipate the terminals, as is done by the vol- 

 taic arc. 



An apparatus, to which M. Despretz was kind enough to call 

 my attention recently at Paris, seemed to promise me some aid 

 in this respect. It was constructed by M. Ruhmkorff, on the 

 ordinary plan for producing an induced current, viz. a coil of 

 stout wire round a soft iron core, with a secondary coil of fine 

 wire exterior to it, having an ingenious self-working contact 

 bi'caker attached ; from the attention paid to insulation in the 

 construction of this apparatus, very exalted effects of induction 

 coiUd be procured. Thus in air rarefied by the air-jjump, an 

 aurora or discharge of 5 or G inches long could be obtained from 

 the secondary coil, and in air of ordinai'y density a spai'k of one- 

 cigiith of an inch long. 



I procured one of these apparatus from M. Ruhmkorff; the 

 size of the coil portion of the apparatus is C'5 inches long, 4 

 inches diameter; the length of the wires forming the coils are 



