ELECTRO-CHEMICAL POLARITY OF GASES. 359 



state of continual agitation. When the conditions were re- 

 versed and the negative wire immersed, the positive wire being 

 at the surface, similar phenomena ensued, but not nearly in so 

 marked a manner ; the cone was smaller, and its base 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 transmis- 

 sion of electricity partaking of the electrolytic and disruptive 

 discharges. Not possessing a battery of this enormous inten- 

 sity, I have not been able to examine this phenomenon 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 interven- 

 ing 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 extreme ; and I have latterly 

 sought for some modified form of electric discharge which 

 should be intermediate between the voltaic arc and the ordi- 

 nary Franklinic discharge or that from the prime conductor 

 of a frictional machine ; for something, in short, which should 

 yield greater quantitative effects than the electrical machine, 

 but not dissipate the terminals, as is done by the voltaic 

 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. Ruhm- 

 korff, 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-work- 

 ing contact breaker attached ; from the attention paid to insu- 

 lation in the construction of this apparatus very exalted effects 

 of induction could be procured. Thus, in air rarefied by the 

 air-pump an aurora or discharge of five or six inches long 

 could be obtained from the secondary coil, and in air of ordi- 

 nary density a spark of one-eighth of an inch long. 



I procured one of these apparatus from M. Ruhmkorff; 

 the size of the coil portion of the apparatus is 6-5 inches long, 



