144 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Finally, this scheme gives Planck's formula without violating the 

 classical laws determining the electromagnetic field in terms of the 

 motions of electricity. Therefore it can also give an account of many 

 optical phenomena, such as those of the propagation of light through 

 matter, for which Planck's assumptions give no account at all. 



Thus this theory correlates the phenomena of heat radiation, chemi- 

 cal affinities, thermions, photo-electric action, interference and many 

 other optical effects, without the use of a mechanism that is inconsis- 

 tent with known magnitudes. Consequently it may be pardoned for 

 requiring these few arbitrary assumptions. 



With regard to the internal mechanism that produces the emitting 

 oscillations we can say very little, except that our intuition would 

 naturally lead us to suppose that they could not exist. But we are 

 here considering things of an order of magnitude so small that, while 

 imagination is as valuable as ever, our intuition is very unreliable. 

 For, after all, when we predict what a mechanism will or will not do, 

 our predictions are not based ultimately on any ability of our own 

 minds to guess the truth of a question, but rather on the accumulated 

 results of our everyday experience, reenforced perhaps by that of our 

 ancestors, and made more accurate by the results of premeditated 

 experiments in the laboratory. This experience is all with things of 

 visible size, and our intuitions tell us most naturally and emphatically 

 what any mechanism would do if it obeyed the laws of visible things. 



But why should this mechanism obey these laws? An enormous 

 giant, capable of seeing only celestial objects and their motions, would 

 predict everything in terms of inverse square laws of acceleration, 

 and would be very much surprised, on increasing his power of vision, 

 to find how rarely terrestrial objects obeyed such laws. Forces, 

 especially those of friction, would then compel his attention; and they 

 in turn would lay the foundation for another shock when he came to 

 study the kinetic theory, with its frictionless attracting and repelling 

 molecules, and their account of the origin of friction and other forces 

 between larger bodies. Here he would have the sympathy of all 

 students, whose intuition tells them that a roomful of ultramicro- 

 scopic bouncing billiard balls would bounce slower and slower until 

 they settled in a hopeless heap on the. floor. In another step, to the 

 electron theory, the character of the forces changes again, and the 

 phenomenon of inertia, the foundation of the dynamics of larger 

 bodies, is explained as a result of electromagnetic forces. Is it, then, 

 at all surprising if still more of these radical changes are in store for 

 us in studying the ether and the internal mechanism of the magneton? 



