78 Mr. James Rice on 



states ; the ehaiice of the resonator emitting at the energy hn is 

 greater than its chance of passing this critical state and radiating 

 at the energy 2 hn, and so on. Planck assumes a certain law of 

 chance for the attainment of these successive stages which is 

 plausible enough ; but one point must be most strongly emphasized ; 

 for it is vital in his reasoning. At whatever multiple of the 

 quantum radiation occurs, the whole amount pours out suddenly ; 

 nothing can check or prevent this total radiation. Here is the 

 very essence of the discontinuity. 



The particular form of the hypothesis Avhich I have outlined 

 above is not the only one possible, in fact it is not quite the foim 

 first propounded by Planck himself. Also other workers have 

 abandoned the particular radiating mechanism postulated by 

 Planck, viz., the resonator, and employed the ordinary orbital 

 whirls of electrons. But all have to assume somewhere or other 

 this feature of discontinuous emission of energy from whatever 

 radiating mechanism they employ. It is possible to do without 

 discontinuous absorption, but discontinuous emission there must 

 be and in amounts which must be multiples of the quantum of 

 energy corresponding to the frequency of the mechanism. 

 Perhaps you may think that because of the extreme smallness 

 (compared to our customary standards) of a quantum of 

 energy even for very high frequencies (an amount equal to 

 about six billionths of an erg [6 x 10"^^] for a frequency of 

 1,000 billions [lO^'^J, that discontinuous outputs in such exiguous 

 quantities would practically amoimt to continuity. Such a view 

 cainiot be maintained. It must be remembered that the scale 

 of dimensions we are dealing with here is quite distinct from that 

 of daily phenomena which appeal directly to our senses. It is all 

 a matter of comparison, and the (luantum which I have just 

 mentioned is certainly 100 times as great as the average heat 

 energy of a molecule at normal temperatures, and it is this latter 

 amount which is the natural quantity of energy for us to consider 

 when we are concerned with the comparative largeness or small- 

 ness of the amount of energy which is converted from one form 



