THURSDAY, OCTOBER 30, 1913.. 
RADIATION THEORIES. 
Vorlesungen iiber die Theorie der Wéarmestrahl- 
ung. By Dr. Max Planck. Zweite Auflage. 
Pp. xii+206. (Leipzig: J. A. Barth, 1913.) 
Price 7 marks. ‘ 
er first edition of this’ book, which ap- 
peared in 1906, was reviewed in NATURE 
(October 11, 1906, Supplement iii.). The many 
and varied contributions to our knowledge of 
radiation phenomena that have been published in 
the ensuing seven years have made it necessary 
for Dr. Planck to rewrite and modify the book 
to a considerable extent, so that it now contains 
many novel features. As before, the object of 
the book is to apply the statistical methods pre- 
viously used in the kinetic theory of gases to the 
phenomena of radiation, and full use is made of 
Boltzmann’s views on the interpretation of 
entropy in connection with the theory of prob- 
ability. But the present treatment is largely based 
on the remarkable assumption which the author 
designates as the “quantum-hypothesis.” 
The property thus assumed for the elementary 
electrical oscillators under consideration may 
perhaps best be explained by comparing them to 
the cisterns, of which many have been invented 
and which are so arranged that when the water 
in them reaches a certain level they overturn and 
empty themselves, then returning to their original 
position to be refilled. In other words, absorption 
takes place continuously, while emission occurs 
intermittently when the energy of the oscillator 
attains one or other of certain discrete values. 
This “quantum hypothesis,” as the author points 
out, is analogous to the electron theory, which 
assigns a definite magnitude to the electron or 
“elementary quantum ” of electricity. It accounts 
for Nernst’s observed phenomena, and, further, 
it is in accordance with the view that every 
different radiation corresponds to a certain definite 
temperature, and it is already beginning to form 
an important element in present-day physical 
researches. 
It need scarcely’ be pointed out that the quantum 
hypothesis entails irreversibility and thus over- 
comes a difficulty of the kinetic theory of gases, 
namely, that even statistical methods apparently 
fail to account for irreversible phenomena when 
applied to a system the elements of which are 
subject to the equations of reversible dynamics, 
unless some further assumption is made (“ Assump- 
tion A” of the late Mr. Burbury), It will thus 
be seen that the present method does not pretend 
to afford a so-called “dynamical proof” of the 
NO. 2296, VOL. 92] 
NA LORE 
261 
phenomena of radiation, and in the preface Dr. 
Planck distinctly expresses the view that a new 
principle cannot in general be represented by a 
model working according to old laws. It will also 
be evident that brief indications of the new method, 
such as those contained in this notice, cannot be 
regarded as adequate descriptions of the real 
substance of Dr. Planck’s investigations. 
It was natural that a theory fraught with such 
far-reaching consequences should attract consider- 
able attention at the recent meeting of the 
British Association, and the occasion was the 
more suitable as the presidency of Sir Oliver Lodge 
had attracted to the meeting a number of physic- 
ists all keenly interested in radiation theories. It 
would be undesirable to refer in greater length 
to these discussions, as they will be dealt with 
elsewhere. A popular account of modern radia- 
tion theories, including special reference to Dr. 
Plancks quantum hypothesis, was given by 
Dr. Max Born, of Gottingen, in Die Naturwissen- 
schaften 21, for May 28, p. 499. 
It does not appear to the present reviewer that 
the quantum hypothesis is necessarily irrecon- 
cilable with dynamical principles. If we take the 
equations of motion of a dynamical system and 
write down the expressions for the second differ- 
ential coefficients of the squares and products of 
its velocities, we obtain formule which may be 
said to determine the energy accelerations of the 
system in the same way that the ordinary equa- 
tions of motion determine the accelerations of 
the masses. If we assume conditions of statistical 
equilibrium we find a definite amount of energy 
associated with a definite system, and we further 
find that certain conditions must hold in order 
that energy equilibrium may be possible. Such a 
method establishes a kind of principle of duality 
between the properties of matter and the properties 
of energy, and is distinctly favourable to 
an atomic theory of energy. But the attempt to 
reduce everything to dynamics would of course land 
us in the old difficulty over the irreversibility. 
GHB 
CHEMICAL TEXT-BOOKS. 
(1) Osmotic Pressure. By Prof. A. Findlay. Pp. 
vi+84. (London: Longmans, Green & Co., 
1913:)' Price 2s. 6d. net. 
(2) The Organometallic Compounds of Zinc and 
Magnesium. By Dr. Henry Wren. Pp. viii+ 
100. (London: Gurney and Jackson, 1913.) 
Price 1s. 6d. net. 
(3) The Chemistry of Dyeing. By Dr. J. K. 
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K 
