594 
with, a dark Iberian people, who in their turn had 
imposed a Mediterranean speech on the still 
earlier Mongoloids, Australoids, and Basques of 
Paleolithic Ireland’’ (p. 74). There is scarcely a 
statement in this sentence which is not open to 
criticism. Many remarks, too, in the chapter on 
“Racial Problems ” are on a par with this. Sir 
Harry is always interesting and suggestive, and 
the book should be widely read in spite of the 
fact that some of the statements do not represent 
the conclusions to which most anthropological 
investigators have arrived. Those in authority in 
our own Empire and in foreign countries should 
read the final chapter on “The Preservation of 
Fauna and Flora.” 
Trattato di Chimica Organica Generale e Applicata 
all’ Industria. By Prof. Ettore Molinari. 
Second edition. Pp. xxiii+1087. (Milan: 
Ulrico Hoepli, 1912.) Price 18 lire. 
Tue first edition of this work, reviewed in NATURE 
in 1910 (vol. lxxxiv, p. 170), was so rapidly ex- 
hausted that within two years of its publication a 
new edition was called for. In preparing this, not 
only has the old text been carefully revised, but 
upwards of 100 pages of new matter have been 
added; the principal sections which have been 
enlarged are those dealing with the manufacture 
of coal-tar, of dyes and colouring matters, and 
the alkaloids; the statistical information, which 
was so novel and useful a feature of the first 
edition, has been corrected to 1910, and where 
possible to 1911. Some interesting information 
(and criticism), for instance, is given under this 
heading of the recent operations of the Camera 
Agrumaria in Sicily in endeavouring to control 
prices of the raw material of the citric acid in- 
dustry. There is no doubt, as proved by the 
rapid exhaustion of the first edition, that such a 
work meets a long-felt want, and we are glad to 
note that an English translation by Mr. T. H. 
Pope is shortly to be issued; a German transla- 
tion is also being prepared by Prof. Siebert. 
Wwe Ja\5 ID)- 
Peeps at Industries: Rubber. By Edith A. 
Browne. Pp. viii+88+plates. (London: A. 
and C. Black, 1912.) Price 1s. 6d. net. 
Tuis book is intended to give the general reader 
a popular account of the rubber-growing industry. 
After a picturesque account of the discovery of the 
utility of rubber, he is taken successively through 
the regions of Brazil and Central America, and 
made to realise vividly the conditions under which 
rubber is produced in each country. The sources 
of the different American and African wild rubbers 
are described, and a graphic account of the collec- 
tion of gutta-percha and balata is also given. 
The reader then learns how Mr. H. A. Wickham 
succeeded under great difficulties in transporting 
some Para rubber seeds from Brazil to Kew, and 
how these have given rise to the vast rubber 
plantations in the Middle East. All the processes 
involved in the production of raw rubber are 
described in non-technical language, and will be 
readily understood by anyone. 
The book is singularly free from literary slips, 
NO. 2231, VOL. 89] 
NATURE 
[AuGusST I, 1912 
but the phrase “Britain, England, Holland, and 
Germany ” (p. 42) has apparently been overlooked. 
The twenty-four excellent illustrations add con- 
siderably to the value of the book, which is 
heartily recommended to anyone desiring a non- 
technical account of rubber production. 
Atlas typischer Spektren. By Prof. J. M. Eder 
and Prof. E. Valenta. Pp. xv+143+ 53 plates. 
(Vienna: Alfred Hélder, 1911.) (Kaiserliche 
Akademie der Wissenschaften.) Price 90 marks. 
Tuts publication contains the results of the study 
and reduction to wave-lengths of the lines in the 
flame, arc, and spark spectra of many of the 
chemical elements. In all, thirty elements are 
dealt with for the flame spectrum, sixty-six for the 
are spectrum, and sixty-eight for the spark spec- 
trum. In general, the region of spectrum dis- 
cussed extends from about A 2400 to about A 7000. 
The lists of lines given are not overburdened 
with the great number of extremely weak lines 
which occur in the spectra of some of the 
elements, but this exclusion of the weakest lines 
does not detract from the value of the work. 
In addition to the text and tabular lists of wave- 
lengths, there are fifty-three excellent helio- 
gravure plates of the various spectra. On these 
a wave-length scale is given showing every 
hundredth tenth-metre. The chief lines shown in 
the plates have the wave-length numbers placed 
opposite them, which makes the identification 
easy, and thus greatly enhances the usefulness of 
the publication. The wave-lengths of the lines in 
the lists are given to the nearest hundredth of a 
tenth-metre. One has no hesitation in pronouncing 
this to be by far the most complete and useful 
collection of laboratory spectra yet published, and 
the library of any practical chemist, physicist, or 
spectroscopist will be incomplete without it. 
LETTERS TO TEE ED TiO 
[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.] 
Some Optical Experiments. 
DurING some recent work I had occasion to try 
the following experiments, the results of which are, 
I trust, of sufficient interest to be recorded in your 
columns. 
Exp. 1.—Take a dise of white cardboard about 
36 in. diameter and draw thereon a series of black 
rings 4 in. wide and 1 in. apart, leaving a central 
disc (white) 2 in. diameter. Hang this on the wall 
of a room fitted with a central cluster of three electric 
lights. Each light should be on a separate switch; 
one light should be of too cp., one of 50 cp., and 
one of 8 cp. With all the lights on, gaze steadily 
at the central white disc from a distance of 3 ft. 
for about fifteen seconds, when an assistant should 
switch out the roo-cp. lamp. The whole disc will 
for amoment be invisible; then the central white spot 
only will reappear. . After an interval of about ten 
seconds the outer white ring will reappear, followed 
by the others in succession towards the centre, until 
the whole disc is visible. 
