Franklin, Dufay a7id Ampere. 481 



electricity, is enormous. It has been generally considered, 

 that as a protection against lightning, the same weight of 

 metal employed as a pipe, would be more efficacious than in 

 the usual solid form of a lightning rod; yet this law does not 

 hold good with respect to galvanic discharges, which are not 

 expedited by a mere extension of conducting surface. Inde- 

 pendently of the augmentation of conducting power, conse- 

 quent to radiation and contact with the air, the cooling influ- 

 ence of which, according to Davy, promotes galvano-electric 

 conduction, a metallic ribbon does not convey a galvanic dis- 

 chai'ge better than a wire of similar weight and length*. 



66. Agreeably to the considerations above stated, the sec- 

 tional area of a conductor remaining the same, in proportion 

 as any statical accumulation which it may discharge is greater, 

 the effects are less superficial ; and the aethereo-ponderable 

 atoms are affected more analogously to those exposed to gal- 

 vanic discharges. It is in this way that the discharge of a 

 Leyden jar imparts magnetic polarization. Thus, on the one 

 hand, the electro-aethereal matter being polarized and greatly 

 condensed, combines with and communicates polarization, and 

 consequently magnetism, to aethereo-ponderable bodies; while, 

 on the other hand, these, when polarized by galvanic reaction, 

 and thus rendered magnetic, communicate polarity to the 

 electro-eether. Hence statical electricity, when produced by 

 galvanism, and magnetism, when produced by statical electri- 

 city, are secondary effects. 



67. Where a wire is of such dimensions, in proportion to 

 the charge, as to be heated, ignited, or dispersed by statical 

 electricity, there seems to be a transitory concentration of the 

 electric power, which transforms the nature of the reaction, 

 and an internal wave of electro-ponderable polarization, simi- 

 lar to those of galvano-electricity, is the consequence. 



68. As above observed (31), the current produced by the 

 magneto-electric machine has all the attributes of the galvano- 

 electric current; yet this is altogether a secondary effect of 

 the changes of polarity in a keeper, acting upon a wire solely 



* It is well known that Wollaston effected the decomposition of water 

 by the aid of a powerful electrical machine. Having enclosed platina wires 

 within glass tubes, these were fused so as to cover the ends. The glass 

 was afterwards so far removed, by grinding, as to expose minute metallic 

 points to the liquid. Under these circumstances, the electricity conveyed 

 by the wires, being preventeil from proceeding over them superficially, was 

 obliged to make its way through the a'thereo-ponderable matter of which 

 metals consist (38). Instead of proving the identity of galvanism with 

 frictional eletricity (note .'59), this experiment shows that in one character- 

 istic at least there is a discordancy. At the same time it may indicate that 

 aethcreal rnay give ilse to aethereo-ponderable undulations. 



Phil. Mag. S. 3. No. 218. SiippL Vol. 32. 2 I 



