FEBRUARY 5, 1914] 
dealt with, examples of practical application 
being furnished by the manufacture of sulphuric 
acid, the Deacon process for chlorine, and the 
drying of linseed oil. Special cases depending on 
the law of mass action are found in the production 
of nitric acid and of ether, and in the caustifica- 
tion of sodium carbonate. The rest of the book 
is chiefly concerned with applications of the phase 
rule to manufactures, for example, lime-burning, 
lead roasting, blast-furnace reactions, and the 
Solvay ammonia-soda process. Technical chem- 
ists and students would often find the book useful 
and suggestive. 
OUR BOOKSHELF. 
Meteorological Office. The Observer’s Handbook, 
1913. Pp. xxiv + 157 + plates. (London: 
H.M. Stationery Office, 1913.) Price 3s. 
Tue issue of an annual edition of this work, 
arranged in 1909, was very appropriate—from a 
scientific point of view—owing to the rapid ad- 
vance of meteorological research in recent years. 
The progress of aérial navigation and the pro- 
_ posed general extension of the centimetre- 
_ gram-second system of units to meteorological 
measurements give greater force to the desira- 
bility of the arrangement. The work is divided 
into four principal sections, most carefully pre- 
pared with due regard to requirements of 
observers and to decisions of international con- 
ferences. Part i. relates mostly to normal 
climatological stations and to non-instrumental 
observations. The articles referring to modifica- 
tions of aqueous vapour and to optical pheno- 
mena are especially interesting. Parts ii. and iii. 
deal with self-recording and additional instru- 
ments, special attention being given to the attain- 
ment of accuracy in their working. Part iv. 
contains reduction and conversion tables, includ- 
ing those adapted for the c.g.s. system. An 
introductory memorandum on the proposed new 
units, to be used for bringing meteorology into 
line with allied sciences, is most useful. Cer- 
tainly the learning of them “does involve a definite 
effort to begin with,” but the proposed regradua- 
tion of instruments will, as pointed out elsewhere, 
probably remove the main objection to the innova- 
tion. 
T_T 
Handbuch der Hygiene. Herausgegeben von 
Prof. M. Rubner, Prof. M. v. Gruber, and Prof. 
M. Ficker. III. Band 3. Abteilung. Die 
Infektionskrankheiten. Pathogene _ tierische 
Parasiten. (Protozoen, Wiirmer,  Glieder- 
fiissler.) Pp. 392+plates. (Leipzig: S. Hirzel, 
1913.) Price 24 marks. 
FOLLOWING upon an introduction of fourteen 
pages dealing with the general problems of para- 
sitology, the book is divided into three sections 
dealing with parasitic protozoa (224 pp.), worms 
(ror pp.), and arthropods (28 pp.), the last section 
being written by W. von Schuckmann, and the 
rest of the book by Th. von Wasielewski. Each 
NO. 2310, VOL. 92| 
NATURE 
629 
section is accompanied by reference to the main 
literature on the subject of which it treats. The 
book is excellently illustrated by means of thirty- 
two coloured plates and 192 text-figures, many 
of which are original. 
The section on protozoa deals in the main with 
the forms which are parasitic in man, the subjects 
of trypanosomiasis, leishmaniasis, ameebiasis, 
malaria, and balantidium-dysentery being treated 
of at length. A short section deals with organisms 
doubtfully related to protozoa—Spirocheta, Haplo- 
sporidia, and Chlamydozoa. The section on 
worms also deals mainly with the species which 
are parasitic inman. Compared with these sections 
the one on arthropoda appears distinctly inade- 
quate, the illustrations being mostly bad and anti- 
quated. The legends to figures of Heematopota 
and Stomoxys (p. 76) are unfortunately reversed. 
Due credit is given throughout to the sources 
whence illustrations are borrowed. An annoying 
custom in bibliographies to German publications 
may be noted in that “Ders.” and “Dies.” 
printed in the same type as authors’ names, are 
used instead of dashes beneath the name or names 
heading the first title—this is most distracting to 
the eye. 
Prof. von Wasielewski may well be congratu- 
lated upon his excellent treatise, which will prove 
most useful to hygienists, for whom the ‘“ Hand- 
buch der Hygiene” is primarily intended. 
G. H. F. Nutra. 
LETTERS 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 ts 
taken of anonymous communications.] 
The Pressure of Radiation. 
I guiTe agree with Mr. C. G. Darwin’s opinion, 
expressed in Nature of January 22, that Boltzmann’s 
proof of the fourth-power law, taken as he gave it, 
or as it is usually given in the text-books, cannot be 
applied as it stands to each separate frequency, because 
the adiabatic expansion, employed in performing the 
cycle, will bring the Doppler effect into play, and 
cause a small change in the frequency, thus confusing 
the issue. But I think the reason of this is that the 
proofs usually given assume too much, and neglect an 
essential point, expressly emphasised by Carnot him- 
self in the application of his principle to the case of 
a saturated vapour. According to my view, the appli- 
cation of Carnot’s principle to a single frequency 
should run somewhat as follows. 
Since the emission of radiation of constant fre- 
quency, independent of the temperature, is a char- 
acteristic property of matter, we are justified, for the 
purpose of argument, in assuming an ideal cylinder 
and piston of a material capable of emitting only a 
single frequency, or a narrowly restricted range. 
Generate a finite volume v of radiation in such a 
cylinder at a constant temperature T and pressure p. 
The work done on the piston is pv, and the total heat 
absorbed E+ v, where E is the intrinsic energy of 
the radiation generated. Cool the cylinder at con- 
stant volume through an infinitesimal range, dT, by 
abstracting heat CdT, where C is the thermal capacity 
