82 Mr. H. Wilde's Experimental Researches 



equal increments of a given force to a body, the effects produced 

 are entirely the reverse of those which, without experiment, 

 would have been predicted; and it is only by the employment 

 of a peculiar order of analogies, drawn from a wide range of phy- 

 sical phenomena, that the appearance of these effects in any new 

 condition of things can even be suspected. A remarkable in- 

 stance of the principle of inverted action here alluded to is that 

 in which a thin plate or disk of metal, when presented to a jet 

 of air escaping under strong pressure from an orifice in a 

 plane surface, is attracted to, instead of being repelled from, 

 the flat surface from which the air issues*. The continued ad- 

 dition of equal increments of heat to a body likewise furnishes 

 many examples of these inversions ; but it will be sufficient to 

 mention the spheroidal condition of water in relation to evapora- 

 tion to indicate the bearing which these remarkable facts have 

 upon the phenomena to be hereafter described. 



89. A consideration of many such examples of inverted action 

 as those above referred to led me to suspect that similar actions 

 might exhibit themselves in those departments of electrical 

 science which have hitherto only been explored with apparatus 

 of a limited range of power. In this expectation I have not 

 been disappointed ; for, with the powerful electromotors which I 

 have had the good fortune to command, I have not only suc- 

 ceeded in clearing up several points of doubtful knowledge re- 

 specting the electric condition of the earth, and of electrolytic 

 action generally, but I have also discovered some new electro- 

 chemical facts in connexion with the electrolyzation of water 

 which must ultimately lead to an important modification of our 

 present ideas on the nature of that substance. 



90. The experiments which I now purpose to give an account 

 of were made in the course of an inquiry into the possibility of 

 transmitting electric signals through metallic cables submerged 

 without an insulating envelope. This inquiry involved, as a 

 preliminary investigation, a consideration of the function which 

 the earth performs as a conductor of electricity when employed 

 for telegraphic purposes; but before giving an account of this 

 investigation, I will briefly state the opinions respecting the elec- 

 tric condition of the earth as already put forth. 



91. At the time when voltaic electricity was first employed 

 for transmitting intelligence to distant places, it was generally 

 believed that a complete metallic circuit, involving the use of 

 two line wires, was absolutely necessary for that purpose, until 

 Steinheil, in 1837, made the discovery that one of these wires 

 might be dispensed with, provided each extremity of the other 



* Manchester Memoirs, new series, vol. v. p. 208. Philosophical Maga- 

 zine, S. 2. vol. v. p. 250. 



