Experimental Researches in Electricity. 15 



it is the most perfect conductor ; in the one insulation is 

 essential ; in the other it is fatal. In comparison of the 

 quantities of electricity produced, the metal machine does 

 not at all fall below the glass one, for it can produce a 

 current capable of deflecting the galvanometer needle, 

 whereas the latter cannot. It is quite true that the force of 

 the current thus evolved has not as yet been increased so as 

 to render it available in any of our ordinary applications of 

 this power ; but there appears every reasonable expectation 

 that this may hereafter be effected : and probably by several 

 arrangements. Weak as the current may seem to be, it is 

 as strong, if not stronger, than any thermo-electric current : 

 for it can pass fluids, agitate the animal system, and, in the 

 case of an electro-magnet, has produced sparks." From 

 the rotation of a plate transition was made to that of a 

 metallic globe, and as in this the currents are nowhere inter- 

 rupted, it was natural to anticipate powerful effects. Nor did 

 disappointment ensue, for although the brass ball employed 

 was only four inches in diameter, and turned merely by the 

 hand, the needle became immediately affected, and by vary- 

 ing the form of experiments, the deflections caused were in 

 all cases such as to prove that the needle was influenced 

 solely by electrical currents in the substance of the ball. 

 These results suggested an experiment of extreme simplicity, 

 of which Faraday remarks : " The exclusion of all extraneous 

 circumstances and complexity of arrangement, and the dis- 

 tinct character of the indications afforded, under this single 

 experiment, are an epitome of nearly all the facts of magneto- 

 electric induction." We cannot therefore do better, since its 

 details are very brief, than give it at length. " A piece of 

 common copper wire about eight feet long, one-twentieth of 

 an inch in thickness, had one of its ends fastened to one of 

 the terminations of the galvanometer wire, and the other end 

 to the other termination ; thus it formed an endless continu- 

 ation of the galvanometer wire ; it was then roughly adjusted 



