io6 Traces of Unity in the Various 



gravity, perhaps, being there all in all. And if so then 

 light must be regarded, not as a separate entity, but as 

 some other force modified under particular circumstances. 

 Indeed, there is no very obvious reason why all that has 

 been said of heat may not be said equally of light, and 

 why heat and light and the force of gravity should not 

 be held to be, not distinct forces, but correlated aspects 

 of one and the same force. 



So too with that working of the solar ray which 

 displays itself in the direction of chemical affinity. It is 

 scarcely possible to think even of referring this to any 

 distinct force : it is not difficult to believe that it may 

 have to do with light or heat, or with the force of gravity, 

 as an altered mode of motion, and nothing else. At all 

 events, there can be no possible reason for thinking that 

 any valid objection to the doctrine of correlation is to be 

 found in the way in which chemical affinity is related to 

 the solar ray. 



Nor is this conclusion at variance with the facts 

 which have yet to be considered. 



The investigations of the last few years have brought 

 to light certain fluctuations and oscillations in atmo- 

 spheric electricity which are full of interest in the present 

 enquiry. Every day there are two maxima and two 

 minima of potential, one maximum between 8 A.M. and 

 ii A.M., the other between 7 P.M. and n P.M., one 

 minimum between 3 P.M. and 7 P.M., the other between 

 II P.M. and 3 A.M. Atmospheric electricity, in fact, 

 exhibits tidal movements closely corresponding with 

 those to which the barometer bears witness, and pointing 

 not less unequivocally to the action of the sun and 

 moon upon the earth. Moreover, the fact that the under 

 and upper surfaces of the atmosphere are in opposite 

 electrical conditions may serve to bring out the same 



