August 27, 1909] 



SCIENCE 



267 



puscle has 8 X 10"^ ergs of energy; this is 

 on the supposition that the usual expres- 

 sions for the energy of a charged body hold 

 when, as in the ease of a corpuscle, the 

 charge is reduced to one unit. Now in one 

 gram of hydrogen there are about 6 X lO^' 

 atoms, so if there is only one corpuscle in 

 each atom the energy due to the coi-puscles 

 in a gram of hydrogen would be 48 XlO^® 

 ergs, or 11 X 10° calories. This is more 

 than seven times the heat developed by one 

 gram of radium, or than that developed by 

 the burning of live tons of coal. Thiis we 

 see that even ordinary matter contains 

 enormous stores of energy; this energy is 

 fortunately kept fast bound by the cor- 

 puscles; if at any time an appreciable 

 fraction were to get free the earth would 

 explode and become a gaseous nebula. 



The matter of which I have been speak- 

 ing so far is the material which builds up 

 the earth, the sun, and the stars, the matter 

 studied by the chemist, and which he can 

 represent by a formula ; this matter occu- 

 pies, however, but an insignificant fraction 

 of the universe, it forms but minute islands 

 in the great ocean of the ether, the sub- 

 stance with which the whole universe is 

 filled. 



The ether is not a fantastic creation of 

 the speculative philosopher; it is as essen- 

 tial to us as the air we breathe. For we 

 must remember that we on this earth are 

 not living on our own resources ; we are de- 

 pendent from minute to minute upon what 

 we are getting from the sun, and the gifts 

 of the sun are conveyed to us by the ether. 

 It is to the sun that we owe not merely 

 night and day, springtime and harvest, but 

 it is the energy of the sim, stored up in 

 coal, in waterfalls, in food, that practically 

 does all the woi-k of the world. 



How great is the supply the sun lavishes 

 upon us becomes clear when we consider 

 that the heat received by the earth under 

 a high sun and a clear sky is equivalent, ac- 



cording to the measurements of Langley, to 

 about 7,000 horse-power per acre. Though 

 our engineers have not yet discovered how 

 to utilize this enormous si;pply of power, 

 they will, I have not the slightest doubt, 

 ultimately succeed in doing so; and when 

 coal is exhausted and our water-power in- 

 adequate, it may be that this is the source 

 from which we shall derive the energy nec- 

 essary for the world's work. When that 

 comes about, our centers of industrial ac- 

 tivity may perhaps be transferred to the 

 burning deserts of the Sahai-a, and the 

 value of land determined by its suitability 

 for the reception of traps to catch sun- 

 beams. 



This energy, in the interval between its 

 departure from the sun and its arrival at 

 the earth, must be in the space between 

 them. Thus this space must contain some- 

 thing which, like ordinary matter, can 

 store up energy, which can carry at an 

 enormous pace the energy associated with 

 light and heat, and which can, in addition, 

 exert the enoi'mous stresses necessary to 

 keep the earth circling round the sun and 

 the moon round the earth. 



The study of this all-pervading substance 

 is perhaps the most fascinating and impor- 

 tant duty of the physicist. 



On the electromagnetic theorj' of light, 

 now vmivei*sally accepted, the energy 

 streaming to the earth travels through the 

 ether in electric waves ; thus practically the 

 whole of the energy at our disposal has at 

 one time or another been electrical energy. 

 The ether must, then, be the seat of elec- 

 trical and magnetic forces. We know, 

 thanks to the genius of Clerk Maxwell, the 

 founder and inspirer of modern electrical 

 theory, the equations which express the re- 

 lation between these forces, and although 

 for some purposes these are all we require, 

 yet they do not tell us very much about the 

 nature of the ether. 



