1hO 
NATURE 
[APRIL 4, 1912 
That section of the book dealing with the iron- 
carbon alloys is, as in the original German edition, 
far the most satisfactory; the treatment is clear 
and concise, although here also the latest develop- 
ments are disregarded. A special word of praise 
is, however, demanded by the splendid photo- 
micrographs with which this portion, and indeed 
the whole of the metallographic section, is illus- 
trated. Both as regards the original photographs 
and the typographical reproduction, practical per- 
fection has been attained—and, indeed, these 
photo-micrographs almost deserve the lavish 
setting of black margins and wide white spaces 
with which they are adorned. 
The remaining portions of this volume, dealing 
mainly with inorganic acids, follow closely on the 
lines of the previous edition, and call for little 
special comment, except as regards the sections 
dealing with the estimation of carbon in steel. 
Here the simplest and most trustworthy of the 
available methods—that of direct combustion in 
oxygen—has not even been mentioned, while the 
various risks of error attaching to the other 
methods described are entirely ignored. 
The perusal of the volume as a whole raises the 
question whether these large compilations really 
serve any useful purpose; they attain huge dimen- 
sions by endeavouring to cover the entire ground 
of technical chemistry so far as analyses and tests 
are concerned, and yet the treatment of each sub- 
ject is limited and is liable to become one-sided 
and inadequate. It would seem that with the 
huge dimensions now attained by the various 
branches of the subject, the day of the general 
handbook has passed, and the era of the special 
monograph has dawned. 
A HANDBOOK OF. PHOTOTELEGRAPHY. 
Handbuch dey Phototelegraphie und Tetauto- 
graphie. By Profs. Arthur Korn and Bruno 
Glatzel. Pp. xvi+488. (Leipzig: Otto 
Nemnich, 1911.) Price 28 marks. 
HIS is a book which, by reason of its 
thoroughness and its exhaustive treatment 
of matters which bear upon the main subject, 
must be recognised as the standard work of refer- 
ence on phototelegraphy for a long time to come. 
Such an immense amount of work has been done 
in this branch of telegraphy that the book must 
be regarded to a great extent as historical, for 
even Prof. Korn himself quickly rendered his own 
selenium apparatus obsolete by the rapid improve- 
ments effected in his telautograph. 
The first chemical telegraph of Alexander Bain 
came really before its time, as although a‘ suitable 
system has been based upon it for the transmis- 
NO. 2214, VOL. 89] 
sion of half-tone photographs, half-tone photo- 
graphs did not exist in 1843, when Bain started 
his experiments. Much of the apparatus for 
telegraphing pictures and photographs is, in fact, 
seen from Prof. Korn’s work to have been the 
practical outcome of extensive experiments made 
originally for the purposes of ordinary word 
telegraphy. 
The book is rendered of the highest possible 
practical value on account of the large number of 
diagrams and illustrations, particularly those relat- 
ing to constructional points, and those who are 
to any extent conversant with the practical diffi- 
culties of picture-telegraphy may perhaps wish that 
still more space had been reserved for the discus- 
sion of the modern apparatus. 
Perhaps the most interesting portion of the bool 
is that relating to Prof. Korn’s apparatus for 
transmission by means of selenium. This element 
is undoubtedly destined to find further uses in 
physical measurements, and the excellent worl 
done by the authors in overcoming the inertia of 
selenium under the influence of light should prove 
of considerable value. The short chapter on photo- 
electric cells will, it is to be hoped, be made much 
fuller in a future edition in view of their important 
application to astronomical measurements; some 
data as to the constants of the cells prepared by 
Elster and Geitel would have been welcomed by 
many readers. 
As will be seen from the reproductions of results 
obtained with Prof. Korn’s telautograph, the 
amount of detail that can be obtained in a tele- 
graphed picture is quite remarkable; the trans- 
mitter comprises a metal drum revolving under a 
stylus, the picture being drawn (or photographed in 
line) in insulating ink; this effects the interruptions 
of the current flowing through the telegraph lines, 
which are recorded by a special type of Einthoven 
galvanometer, the metal “string” of which is 
shifted on the passage through it of a weak cur- 
rent, the shift allowing a narrow beam of light to 
pass to the exposing box, where a synchronously 
revolving drum furnished with photographic paper 
is placed. 
The systems or adaptations of Charbonelle, 
Berjeanneau, Belin, Thorne-Baker, and others are 
described, though the reader is not given an oppor- 
tunity to compare their results with those obtained 
by the authors, and brief reference is made to the 
wireless experiments that have been carried out. 
The book is thoroughly up to date, including 
references even to the new system of Prof. 
Tsch6érner, of Vienna, and will be found extremely 
interesting by the many people who are at the 
present time experimenting in the directions dis- 
cussed. abs A, 183. 
