590 THE PKINCIPLES OF SCIENCE. [CHAF. 



it be consistent with the laws of nature; and in such 

 things as these, experiment is the best test of such con- 

 sistency." 



He executed many difficult and tedious experiments, 

 which are described in the 24th Series of Experimental 

 Researches. The result was nil, and yet he concludes : 

 "Here end my trials for the present. The results are 

 negative ; they do not shake my strong feeling of the 

 existence of a relation between gravity and electricity, 

 though they give no proof that such a relation exists." 



He returned to the work when he was ten years older, 

 and in 1858-9 recorded many remarkable reflections and 

 experiments. He was much struck by the fact that elec- 

 tricity is essentially a dual force, and it had always been 

 a conviction of Faraday that no body could be electrified 

 positively without some other body becoming electrified 

 negatively ; some of his researches had been simple de- 

 velopments of this relation. But observing that between 

 two mutually gravitating bodies there was no apparent 

 circumstance to determine which should be positive and 

 which negative, he does not hesitate to call in question an 

 old opinion. " The evolution of one electricity would be a 

 new and very remarkable thing. The idea throws a doubt 

 on the whole ; but still try, for who knows what is possible 

 in dealing with gravity ? " We cannot but notice the 

 candour with which he thus acknowledges in his laboratory 

 book the doubtfulness of the whole thing, and is yet pre- 

 pared as a forlorn hope to frame experiments in opposition 

 to all his previous experience of the course of nature. For 

 a time his thoughts flow on as if the strange detection were 

 already made, and he had only to trace out its conse- 

 quences throughout the universe. " Let us encourage 

 ourselves by a little more imagination prior to experiment," 

 he says ; and then he reflects upon the infinity of actions 

 in nature, in which the mutual relations of electricity and 

 gravity would come into play ; he pictures to himself the 

 planets and the comets charging themselves as they ap- 

 proach the sun ; cascades, rain, rising vapour, circulating 

 currents of the atmosphere, the fumes of a volcano, the 

 smoke in a chimney become so many electrical machines. 

 A multitude of events and changes in the atmosphere 

 seem to be at once elucidated by such actions ; for a 



