THE PATH OF EVOLUTION 



its abstract nature becomes to most men a matter of 

 indifference, or a question of ontological interest only ; 

 and secondly, the inherent difficulties in the attempt ! 

 We are surrounded on all sides by the effects of 

 gravitation, and our every movement and action 

 helped or hindered thereby ; yet it, of all the phenom- 

 ena around us, is the only one that we can in no way 

 change, influence or direct. No human contrivance 

 can increase or diminish its force or its rate of accelera- 

 tive motion. Magnetic attraction, that varies also 

 inversely with the square of the distance, can over- 

 power its force, but only as a cord might drag or 

 hold up a body that else would fall ; but it can in 

 no wise be correlated therewith. Countless experi- 

 ments have been tried by means of heat, chemical 

 action and otherwise, to modify the phenomena that 

 gravitation presents, but all with negative results. 

 It has been impossible to apply inductive and em- 

 pirical reasoning thereto. The only hope of success 

 lies in the deductive method : assuming an a-priori 

 hypothesis and testing its validity by the few known 

 facts we may possess. 



The only hypothesis of the cause of gravitation 

 that, in the opinion of J. Clerk Maxwell, " was in- 

 genious, and that has been so far developed as to be 

 capable of being attacked and defended," has been 

 already mentioned under the title of the Atomic 



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