JUNE 17, 1915] 

NATURE qa 

employed in a discussion of the bearing of the 
electron theory on the problems of temperature 
radiation, magnetism, and the theory of metallic 
conduction. Finally, after an account of the 
theories of spectroscopic phenomena and_ the 
phenomena of radio-activity and X-rays, we are 
led into a discussion of the theories of the con- 
stitution of the atom. 
It will be seen that the book covers a very 
extensive field. To give an adequate representa- 
tion of the entire electron theory is naturally a 
task of the greatest dithculty, but the author 
appears to have done this in an admirable manner. 
Of necessity the treatment is at many points very 
restricted, but almost all points of general interest 
are considered. If any problem is treated more 
fully than others it is the theory of metallic con- 
duction, as might naturally be expected from the 
author’s own work. The exposition is through- 
out very clear and concise, and Prof. Richardson 
possesses a great gift of making even complicated 
arguments very easy for the reader to follow. A 
close connection with the latest experimental pro- 
gress is everywhere maintained, and problems 
which involve hitherto unsolved difficulties are 
treated in a manner very far from being dogmatic. 
In reading Prof. Richardson’s book one gets 
ample opportunity to think about the present state 
of theoretical physics. The collection of the 
numerous brilliant achievements of the electro- 
magnetic theory and the electron theory fills one 
with the greatest admiration. Still, the difficulties, 
first discovered with relation to the problem of 
temperature radiation and later in other problems, 
seem to be so great and of such a fundamental 
character that the theory will need very great 
alterations. Even if a way is indicated by Planck’s 
theory no satisfactory solution of the difficulties 
has yet been found. In text-books only a few 
years old one finds great enthusiasm over what 
was called the future programme of the electro- 
magnetic theory. It was believed that this theory 
constituted a final accomplishment of ordinary 
mechanics, and there appeared to be no limit to 
the application of the general principles of the 
theory. This attitude has changed most decisively. 
The impression obtained by reading the present 
book, however, is anything but merely dis- 
illusioning. Scarcely at any time has our know- 
ledge increased so very rapidly as of late years, 
and, above all, we now possess much more 
powerful methods of experimental attack than 
were dreamed of a short time ago. Especially 
investigation of the radiation from radio-active 
bodies has proved most efficient in disclosing the 
internal structure of the atoms. If at present we 
may speak of a programme for the future develop- 
NO. 2381, VOL. 95] 

ment, it would, perhaps, be to examine the con- 
stitution of the special atomic systems actually 
existing, and then, by means of the directly 
observable properties of matter, possibly to deduce 
the general principles. If so, the evolution would 
be exactly the reverse of that anticipated. 
In the present unsettled state, Prof. Richard- 
son’s book, which gives a balanced and masterly 
survey of a wide range of knowledge, will no 
doubt be especially welcome. It can be most 
heartily recommended, not only to students who 
seek an introduction to the electron theory, but 
to all interested in the modern development of 
physics. News: 
HORTICULTURE AND BOTANY. 
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