302 THK LIMITS OF SCIENCE. 



ultimate end of science, when considering' its forces, is to marshal! 

 them all under one, and say. " This force is the primary force of 

 nature, and all others can be accounted for by it. 1 ' It was no 

 wonder, when Newton made known his great discoveries, that 

 gravity was placed in the front rank among the claimants for 

 this place of honour, but though the announcement of the law of 

 gravity has done so much in enabling us to explain the movements 

 and positions of celestial and terrestial bodes, and has at one step. 

 to a great extent, evolved order out of chaos in the universe, 

 although we owe it to the never-wearying action of this law that 

 the earth is safely held, against its own centrifugal force, from 

 flying off its sunny orbit to unknown regions of space. Still, we 

 seem to have good reason for denying to it the position of honour 

 that it seemed likely to gain. Supposing, however, that gravity 

 is the fundamental force for which we are looking, we have cer- 

 tainly reached the limits of science here, for what explanation 

 can we give of gravity? Why and how do two pieces of matter 

 attract each other directly as their mass and inversely as the 

 square of their distance, when there is no apparent connection 

 between them whatever? I am aware that there are theories, 

 such, for instance, as that of Professor ( )sborne Reynolds, 

 which may prove to be true explanations, but for the 

 present I think we must still say, as Newton himself 

 said : " The cause of gravitation remains undiscovered." 

 But great as gravity is as a source of power in the universe, 

 it seems altogether inadequate and insignificant compared to the 

 energy displayed in other ways. It seems impossible that gravity 

 alone can account for the great velocity of many of the stars, 

 for our own sun, for instance, travelling at the rate of nine to 

 twelve miles a second, or for a star like Arcturus, travelling 400 

 miles in the same time. But if we are not able to account ft ti- 

 the forces of nature, which control the motions of the stars, we 

 seem to be still less able to give a scientific explanation of the laws 

 controlling the almost infinitely greater energy required to 

 explain the various phenomena connected with atoms and mole- 

 cules. What is it that makes these tiny particles cling so tena- 

 ciously? Why should the atoms of which a bar of iron, for 

 instance, is made, hold together, enabling it to sustain enormous 

 weights? If there were not forces to hold them they would 

 assuredly crumble, and our bar would be as dust at the least 

 touch. It is not the force of gravity that holds the particles 

 together. That is nothing like strong enough. Neither is it 

 gravity that makes two or more elements combine to form a 

 compound. We say this is due to the affinity of one element for 

 another, but that is only a euphemistic way of admitting that we 

 do not know what the force is. It is to the electron theory that 

 we must return if we wish to get within sight of greater forces. 

 In my second question — for the sake of clearness I avoided com- 

 ment on their electrical significance — we considered other aspects 

 of the electron, nevertheless the great fundamental property of 



