Marcu 7, 1912] 
NATURE 5 
DESIGN IN ILLUMINATION. 
Principes de la Technique de l’Eclairage. By Dr. 
L. Bloch. Translated by G. Roy. Pp. 183. 
(Grenoble: Jules Rey; Paris: Gauthier-Villars, 
Ig1r.) Price 5 francs. 
HIS book is a translation of Dr. L. Bloch’s 
“Grundziige der Beleuchtungstechnik,” and 
although an interval of four years separates the 
original from the translation, the work was worth 
doing, as the admirable treatment accorded the 
subject by Dr. Bloch will secure a prominent place 
for his treatise in the literature of the subject for 
a long time to come. 
The subject-matter isin strict accordance with 
the title, a condition not too closely observed in 
some text-books on illuminating engineering. The 
author has devoted his attention almost entirely 
to the development of methods of design of light- 
ing installations from given data, whereby the 
results in illumination and costs can be predicted 
with a reasonable degree of certainty. 
In the first chapter fundamental quantities and 
their relations are clearly and accurately dealt 
with, the idea of luminous flux in particular being 
elucidated by a material analogy, which will carry 
conviction to a far larger number of readers than 
will the hardly worked analogy with magnetic 
flux. The author uses throughout the photometric 
notation of the Geneva Congress of 1896. 
Methods for the determination cf mean spherical 
intensity from polar curves of intensity are briefly 
described in the second chapter, including the 
author’s modification of Rousseau’s construction, 
which adapts it for rapid calculation, but the 
equally convenient graphical method due to Ken- 
nelly is not mentioned. 
Some general considerations with regard to 
exterior and interior lighting bring the third 
chapter to a conclusion, great stress being rightly 
laid on the importance of mean hérizontal illumina- 
tion as a factor in design. 
The real business of the book begins in the 
fourth chapter. A method is here given by which 
the integral of the Rousseau curve for a given 
light source over the lower hemisphere is made 
to supply material for a table of total luminous 
flux emitted under any angle from the vertical to 
the horizontal. 
A number of such curves are developed, each 
from the average polar curve of luminous intensity 
of a specified type of source, and all being reduced 
to the same value of mean spherical intensity. 
With the help of these tables, the cosine law, and 
some experimental data on reflection coefficients 
obtained by the author, a complete method of 
design is elaborated, applicable to most conditions 
in modern lighting. The author’s justification for 
NO. 2210, VOL. 89] 
his broad generalisations and approximations 
appears from the comparatively close agreement 
existing between his observed and calculated 
values of illumination in examples taken from his 
practice in the street lighting of Berlin. 
Photometry is dismissed at the beginning of the 
fifth chapter with little more than a description of 
the Brodhun illumination photometer as used by 
the author on the Berlin streets. This is followed 
by a description of a method for reducing to a 
minimum the number of street observations neces- 
sary for the determination of the value of the 
mean horizontal illumination. 
The sixth and last chapter is devoted to indirect 
lighting, and, in spite of obvious difficulties, it is 
shown from actual examples that the formule and 
methods already devised are still able in certain 
cases to give fairly accurate results. It is not 
easy, however, to follow the author in his conten- 
tion that the difference in cost between direct and 
indirect lighting for a given effect achieved may 
be in many cases of very small moment. 
The book is a successful attempt to place the 
design of illuminating installations in a position 
comparable with that held by design in other 
branches of engineering. 
THE PACE OF THE HARTEH. 
La Face de la Terre. By Prof. Ed. Suess. Vol. 
ili., pt. 2. Pp. xii+531-956, 2 maps, 124 figs. 
(Translated under the direction cf E. de Mar- 
gerie.) (Paris: Armand Colin, 191r.) 12 frs. 
HE present instalment of the French edition 
of Prof. Suess’s great work includes only 
the first half of the final volume. It consists of 
translations of chapters x.—xvi., which deal with 
the western representatives of the Altaid mountain 
system of Prof. Suess, and with the Alps, Atlas, 
and various related mountains, which are all 
attributed to foldings within areas surrounded by 
an Altaid framework. The last chapter deals with 
the North Atlantic area, including Iceland and 
Greenland. 
As the original has already been reviewed in 
NATURE, it unnecessary to reconsider the 
problems dealt with in the work. The chapters 
have been translated by MM. H. Baulig. Ch. 
Jacob, and P. Lemoine; the volume is edited by 
M. de Margerie, who is to be warmly congratu- 
lated on the great service he has made to students 
of Prof. by this accurate and 
scholarly translation, and by the issue of this well- 
illustrated edition of the book. 
The study of the work requires such frequent 
reference to geological maps, of which the original 
edition contains so few, that it is difficult to read 
M. de Margerie’s 
is 
work 
Suess’s 
except in a geological library. 
