January 24, 1913] 



SCIENCE 



13S 



Planck has unqualifiedly declared against 

 it, and Einstein gave it up, I believe, 

 some two years ago; and yet a quantum 

 theory which fails completely to interpret 

 or take any account of the most striking 

 and the best established experimental fact 

 which demands a modification of old 

 theories, viz., the independence of the 

 energy of emission of electron upon the in- 

 tensity of the source, or, more generally, 

 the inter-convertibility of ^-rays and ether 

 rays is, at best, a very impotent affair. If 

 we are going to leave either of these two 

 main groups of facts out of account I think 

 almost any experimentalist would say that 

 the first group (that having to do with the 

 universal constant h) can most easily be 

 spared; for if we could have radiant 

 energy localized in space we might possibly 

 account for all the experimental facts with- 

 out having it emitted by a given source in 

 exact multiples of something, but spread- 

 ing ether pulses which contain energy in 

 mi^ltiples of something are certainly wholly 

 inadequate. They go but a short way 

 toward accounting for the present experi- 

 mental situation. In conclusion then we 

 have at present no quantum theory which 

 has thus far been shown to be self-consist- 

 ent or consistent with even the most im- 

 portant of the facts at hand, and yet it 

 looks as though one had to come, and when 

 it comes I can scarcely believe that it will 

 be one of the milder forms. That we shall 

 ever return to a corpuscular theory of 

 radiation I hold to be quite unthinkable. 

 The facts of the static field alone seem to 

 preclude such a possibility. But I see no 

 a priori reason for denying the possibility 

 of assigning such a structure to the ether as 

 will permit of a localization of radiant 

 energy in space, or of its emission in exact 

 multiples of something, if necessary, with- 

 out violating the laws of interference. That 

 no one has as yet been able to do this can 



scarcely be taken as a demonstration that it 

 can not be done. Fifty years ago we knew 

 that such a thing as an atom existed, but 

 we knew absolutely nothing about its struc- 

 ture, and it was customary to assume that 

 it had none. To-day we know a great deal 

 about the structure of the atom, but the 

 position formerly occupied by it has been 

 assumed by that thing which we call the 

 ether. We know that there is a vehicle for 

 the transmission of electromagnetic energy, 

 but we know nothing whatever about its 

 structure and it has been customary to as- 

 sume that it has none. To deny the exist- 

 ence of this vehicle, which we have been in 

 the habit of calling the ether, and to use the 

 word "vacuum" to denote all the proper- 

 ties heretofore assigned to it by the experi- 

 mentalist, viz., those of transmitting electro- 

 magnetic disturbances, is a bit of sophistry 

 in which he is little interested. "We seem 

 to be on the eve of learning something more 

 about the properties of this vehicle, call it 

 bj' what name you will, than we have 

 known heretofore. Certainly there has 

 never been a time when physics offered 

 such tasks to its followers as now, nor ever 

 a time when it needed more and better 

 brains applied to these tasks. It may be 

 that "thou art come to the Kingdom for 

 such a time as this." 



R. A. MiLLIKAN 



University of Chicago 



EDUCATIONAL DIAGNOSIS^ 

 Up till a score of years ago theories of 

 intellectual and moral diagnosis sufliered 

 from two defects. They had not fully 

 abandoned the notion that mysterious inner 

 forces or agents existed — memory, atten- 

 tion, courage, imitativeness, constructive- 



* Address of the vice-president and chairman of 

 Section H — Education — American Association for 

 the Advancement of Science, Cleveland, December, 

 1912. 



