JANUARY 15, 1914] 
NATURE 55 
ios) 
corners and back. Several daily record sheets are | 
provided, and the student is expected to fill these 
up, giving particulars of date, portion of the text- 
book or work studied, remarks, as well as par- 
ticulars of the time which he has spent at other 
subjects. The student is expected to certify this 
record by his signature. Pasted to the interior 
of the cover are elaborate instructions regarding 
methods of entering work done, for filling up the 
record sheet, excuses, collection and distribution 
of work-books, inspection, and corrected work. 
Some of these instructions are distinctly good, 
and might be taken to heart by many teachers of 
mathematics in this country. For example—‘ as 
soon as possible learn to draw a light, smooth, 
draughtsman’s line.”” Those who have had the 
opportunity of examining the British average 
mathematical home-work will appreciate this 
quotation. No doubt the designer of this book 
has found that it meets perfectly the needs of his 
own institution and students, but we question 
whether it will meet with much favour in this 
country, where it is well known that every teacher 
prefers to develop his own methods as regards 
style of home-work, examination, and so on. 
The Celebration of the Two Hundred and Fiftieth 
Anniversary of the Royal Society of London, 
July 15-19, 1912. Pp. 128. (London: Hum- 
phrey Milford, 1913.) Price 5s. net. 
Tue interesting events in connection with the 
celebration of the 250th anniversary of the Royal 
Society in July, 1912, were reported in these 
columns at the time, and the contents of this 
volume consequently cover ground familiar to our 
readers. This permanent record of the proceed- 
ings contains a full list of delegates and verbatim 
accounts of the addresses, speeches, telegrams, 
and letters addressed to the Society from learned 
societies and other bodies throughout the world. 
With the new edition of the “Record” of the 
Society, and the facsimile reproduction of the 
pages of signatures of the fellows in the Charter 
book, from that of the Royal founder down to 
those entered in the summer of 1912, it will form 
an appropriate and lasting memorial of a note- 
worthy celebration. 
Who’s Who in Science: International, 1914. 
Edited by H. H. Stephenson. Pp. xx+662. 
(London: J. and A, Churchill.) Price 2s. net. 
Tus excellent work of reference contains, in 
addition to its 9000 biographies of men of science 
of all nationalities, other useful information. 
Especially convenient are the tabular statements, 
arranged alphabetically, of particulars about the 
universities of the world, which include the names 
in each case of the head of the university and the 
senior occupants of the various scientific chairs. 
A valuable Jist of the ‘‘World’s Societies” is also 
included, and from it the name, address, number 
of members, the name of the secretary, and other 
facts can be seen at a glance. An exhaustive 
classified index adds greatly to the value of the 
volume. 
NO. 2307, VOL. 92] 
| in question cannot be considered 
BEETERS TO THE: EDITOR. 
[The Editor does not hold himself responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of Nature. No notice is 
taken of anonymous communications.] 
The Pressure of Radiation and Carnot’s Principle. 
I GATHER from a letter on this subject which appears 
| in your last issue that Lord Rayleigh endorses the 
opinion that the partial pressure p of any particular 
frequency in full radiation may properly be deduced 
from the intrinsic energy-density E/v of the same 
frequency by Carnot’s principle. 
The other point to which I wished to direct atten- 
tion is that, in the case of a steady stream of radia- 
tion of constant frequency, the heat quantity measured 
is the total heat of formation per unit volume, 
E/v+p, and not the intrinsic energy-density E/v as 
commonly assumed. The disagreement with experi- 
ment of Wien’s well-known formula for the partition 
of energy in full radiation, is readily explained if we 
assume that it represents only the intrinsic energy. 
The corresponding value of the pressure is very easily 
deduced by reference to Carnot’s principle, as Lord 
Rayleigh has indicated. The formula which I have 
proposed (Phil Mag., October, 1913) is simply the 
sum of the pressure and energy-density thus obtained, 
and gives very satisfactory agreement with_experi- 
ment, both for radiation and specific heat. I prefer 
it to Planck’s formula (among other reasons) on the 
ground that the latter cannot be reconciled with the 
classical thermodynamics, and involves the concep- 
tion of a quantum, or indivisible unit of action, which 
is unthinkable. The corresponding physical mag- 
nitude on my theory, which I have elsewhere called 
a molecule of caloric, is not necessarily indivisible, but 
bears a very simple relation to the intrinsic energy of 
an atom, which is all that is required to explain the 
fact that radiation may in special cases be emitted in 
atomic units which are multiples of a particular 
magnitude. H. L. CaLrenpDar. 
Imperial College of Science and Technology, 
South Kensington. 
Atomic Models and X-Ray Spectra. 
In his letter to Nature of January 1 on “ Atomic 
Models and X-Ray Spectra,” Dr. F. A. Lindemann 
deals with the approximate agreement between the 
recent experiments of Mr. H. G. J. Moseley on ‘* The 
High-frequency Spectra of the Elements” (Phil. Mag., 
December, 1913), and the calculations given in my 
paper, ““On the Constitution of Atoms and Mole- 
cules” (Phil. Mag., July, September, November, 
1G13)- 
In Dr. Lindemann’s opinion a theoretical explana- 
tion of Mr. Moseley’s results can be obtained in several 
ways; and he therefore concludes that the agreement 
to support the 
assumptions used in my paper. By the help of a 
consideration of dimensions he seeks a relation be- 
tween the five quantities, v, x, Nne?, m, and h. He 
shows that an infinite number of different expressions 
can be obtained for v in terms of r, Nne*®, m, and h; 
and he indicates how several of these expressions 
may be brought in approximate agreement with the 
experimental results. 
This procedure does not appear to me to be justified. 
Just as little as the five quantities v, r, Nne*, m, 
and h, the four quantities, r, Nne*, m, and h, may 
be considered as independent of each other. By a 
consideration of dimensions we can obtain a relation 
