306 
most of the well-established results of the undulatory 
theory of light. The great difficulty is the reconcilia- 
tion of the two sets of facts. The boldest and simplest 
attempt lies in abandoning altogether present con- 
ceptions of the zther, and relying on some purely 
descriptive principle, such as relativity. But the 
attempt at a dynamical explanation should be made, 
and Mr. Jeans concluded by a suggestion as to the 
meaning of the Planck constant h. This constant is 
connected with e, the charge of an electron. We 
may, perhaps, imagine that the equations of the 
zther involve e or h as well as the Maxwell terms. 
These terms may be eliminated in forming the equa- 
tions for wave propagation for certain cases, and in 
that event there will be no discrepancy between the 
quantum theory and the undulatory theory. But 
where the equations are applied to interactions 
between matter and ether, the older theory will not 
apply, and the terms involving h must remain in. 
The second speaker was Prof. Lorentz. He ac- 
cepted the quantum theory, and sought a method of 
accounting for it. Some kind of discontinuity in the 
transfer of energy is experimentally proved, but the 
individual existence of quanta in the ether is im- 
possible. He considered the scheme of transference 
of energy from matter to resonators and to the ether. 
The transfer from a resonator to the ether of a 
quantum can be easily conceived, but it is difficult 
to understand how the quantum can be transferred 
back to the resonator from the zther, for once in the 
zther it becomes distributed indefinitely. Prof. 
Lorentz suggested that the quanta are necessary in 
some transference, and that perhaps the solution was 
to be found in assuming them operative in transfer- 
ences from matter to the resonator and vice versa, and 
not in the interchange between resonators and the 
zther. The difficulty in this yiew is to distinguish 
clearly the two classes, matter and resonator. Prof. 
Lorentz was again clear and very interesting. His 
humour again appeared, as when referring to Sir J. J. 
Thomson’s atom he remarked that ‘it was highly 
ingenious—as it could not otherwise be—but the 
point was, did it represent the truth?” 
Prof. Pringsheim followed, and confined his 
remarks to the experimental bearing of the problems 
raised. The constants of radiation are not accurately 
enough known—for example, Stefan’s and Planck’s 
constants. He also referred to the question of the 
radiation from other sources than the black body. 
Dr. Bohr, of Copenhagen, was the next speaker. 
His work had been referred to by previous speakers, 
and he gave a short explanation of his atom. His 
scheme for the hydrogen atom assumes several 
stationary states for the atom, and the passage from 
one state to another involves the yielding of one 
quantum. Dr. Bohr also emphasised the difficulty of 
Lorentz’s scheme for distinguishing between matter 
and the radiator. Planck’s resonator has all the 
ordinary properties of matter, and it is difficult to 
keep up the distinction. Prof. Lorentz intervened to 
ask how the Bohr atom was mechanically accounted 
for. Dr. Bohr acknowledged that this part of his 
theory was not complete, but the quantum theory 
being accepted, some sort of scheme of the kind sug- 
gested was necessary. 
Prof. Love represented the older views, and main- 
tained the possibility of explaining facts about radia- 
tion without adopting the theory of quanta. He 
criticised the application of the equi-partition of 
energy theory, on which part of the quantum theory 
rests. The evidence for the quantum theory of most 
weight is the agreement with experiment of Planck’s 
formula for the emissivity of a black body. From 
the mathematical point of view, there may be many 
NO. 2297, VOL. 92] 
NATURE 
[NoveMBER 6, 1913 _ q 
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more formula which would agree equally well with 
the experiments. A formula due to A. Korn was deal 
with, which gave results over a wide range, showing 
just about as good agreement with experiment 
the Planck formula. In further contention that 
resources of ordinary theory are not exhausted, 
pointed out that it may be possible to extend the 
calculation for the emissivity of a thin plate due to. 
Lorentz to other cases. For this calculation no simple — 
analytical expression represents the results over the 
whole range of wave-lengths, and it may well be 
that in the general case no simple formula exists 
which is applicable to all wave-lengths. Planck’s 
formula may, in fact, be nothing more than an ~ 
empirical formula. Lord Rayleigh spoke next. He 
did not attempt to discuss the question, but welcomed — 
the discussion. It was interesting to see Lord Ray- 
leigh at the meeting, and references to his historic — 
work on the subject of radiation were made by 
several of the speakers. 
Sir J. Larmor spoke about the theory of the equi-— 
partition of energy. In an isolated region of the ~ 
zther there is no way open for the interchange of 
energy at all between one type of radiation and ~ 
another, so that the assumption of ‘‘other things 
being indifferent’? is not applicable. The structure — 
of an electron and the mechanism by which it reacts 
with the ether is totally unknown. In the very 
intense kinetic phenomena which occur when trans- 
ferences of energy take place, the energy may not 
be expressible as a sum of squares, as the equi- 
partition theory requires. A transfer may be even — 
discontinuous. Sir J. Larmor went on to show that 
equi-partition need not (therefore be necessary as — 
regards free radiation, and atomic vibrations which 
are set up by its agency and must be in equilibrium 
with it need not come under the equi-partition theory. 
The new knowledge we have of specific heats at very 
low temperatures has also led to further speculations 
and extension of theoretical schemes, but it can be 
held that there is nothing destructive of older prin- 
ciples of physics. He looked to a_ reconciliation 
between the older and newer views from further 
knowledge of the interactions between free zther 
and electrons. 
Sir J. J. Thomson further discussed the equi- 
partition theory, and was prepared to give it up if 
it was the cause of all the difficulty. Referring to 
statistical methods, he recalled De Morgan’s saying 
that if a calculation in probability required more than 
half a sheet of notepaper, its result should not be 
received without further independent evidence. 
Sir Oliver Lodge spoke also, and pointed out’ that 
the ordinary laws could not apply in the interior of 
an electron or a positive charge, for if they did the 
charge would fly to pieces because of the mutual 
repulsion of its parts. 
Prof. Lorentz again spoke, and remarked that a 
theory that explained both the phenomena of specific 
heat and the absorption spectrum was not to be dis- 
posed of on purely mathematical grounds. He em- 
phasised the fact that the Planck constant was there, 
and that it had some very definite meaning which 
had to be interpreted. P 
Dr. S. D. Chalmers gave an account of an atom 
model which agreed with the results of the quantum 
theory, and also with the magneton hypothesis. Mr.° 
Jeans closed the discussion with replies to some 
criticisms, and again pointed out that from the experi-. 
mental point of view Prof. Lorentz’s discrimination” 
of matter and radiators was impossible. No distinc= 
tion between them could be made. 
This discussion went on from ten o’clock to one, 
and the interest was kept up till the end. It was of 
