436 
NATURE 
[MarcH 10, 1904 
plant Remirea maritima and the grass Stenotaphrum 
americanum. Many of the illustrations are limited to 
the study of a single tree or shrub, indeed all in the 
parts which deal with monocotyledonous trees and 
economic plants. 
The editors, Drs. G. Karsten and H. Schenck, have 
provided a very useful and instructive series of plant 
studies, and it is to be hoped that the publishers will | 
be encouraged to arrange further series. To the 
botanist and plant lover, as well as to the student, 
these carefully prepared illustrations should be of very 
great interest, and will help to make more definite the 
written descriptions of travellers. 
Photographic Failures. Prevention and Cure. By 
‘* Scrutator.’’ Pp. 94. 
Photogram by Dawbarn and Ward, Ltd., 1903.) 
Price 1s. net. 
Tue subject of this book will appeal to numerous photo- 
graphers, for many are the pitfalls which they try 
to avoid. 
Negatives may be too hard or too dense, thin, | 
fogged, umsharp, spotted, curiously marked, &c., 
and prints may suffer from many similar blemishes. 
A book that will inform the photographer of the 
remedies that may be applied to the particular fault in 
question is one that should be thoroughly welcomed. 
““Scrutator,’’ of the Photogram, seems to have sup- 
plied this want, and confines his antidotes to the 
problems which beset the practical photographer. The 
method of treatment adopted is to describe each failure, 
fault or defect, then to state the causes to which they 
are due, and finally to suggest either the preventatives 
or the remedies to be employed. In the case of nega- 
tives he gives some specimen negative prints on thin 
transparent paper to show how incorrect exposure and | 
development affect the relative tones. The book is one 
that will be very useful to every photographer. 
Up-to-Date Tables for Use throughout the Empire. 
Weights, Measures, Coinage. Compiled and 
written by Alfred J. Martin. Pp. 251. (London : 
T. Fisher Unwin, 1904.) Price 2s. 6d. 
Tue compiler of this collection of tables believes that 
the adoption of the metric system of weights and 
measures for use within the Empire is near at hand, 
and it is to be hoped his optimism will be justified. 
He maintains ‘‘ that if the metric system were made 
compulsory for railway companies; were adopted by 
the Bank of England; and shown on our Ordnance 
Surveys ; that within a very short time the system would 
be generally adopted throughout the Empire.’’ It is 
unnecessary to do more than mention a few of the 
numerous tables provided. There are tables showing 
the relations of various weights and measures of water 
and of its density at different temperatures; a com- 
parison of British and international systems of physical 
units, and of measures of time. The little book should 
certainly serve to popularise the decimal system. A 
penny supplement for beginners, intended as a guide 
to simple arithmetic and to show how decimals can be 
taught at an early age, is also published. 
By W. G. Borchardt, M.A., 
(London: Rivingtons, 1903.) 
Arithmetical Examples. 
B.Sc. Pp. viii+279. 
Price 3s. 
THESE examples, with the exception of one paper, are 
taken from the author’s ‘‘ Arithmetical Types and 
Examples ”’ recently noticed in these columns. The 
exercises are numerous and well graded, and in draw- 
ing them up Mr. Borchardt has kept the recommend- 
aticns of the Mathematical Association Committee 
before him. 
NO. 1793, VOL. 69 | 
(London: Published for the | 
| 
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 NaturRE. 
No nctice is taken of anonymous communications. | 
Rontgen Rays and the 7 Rays from Radium. 
Ir has been proved by Mr. Strutt that, for the y rays of 
radium, the relative conductivity of gases varies approxi- 
mately as the density, whereas there is a wide divergence 
from this law in the case of Réntgen rays. Taking air as 
the standard, the figures given are :— 
| Density y Rays Réntgen Rays 
| INGE: an ies 1-00 1-00 100 
| Carbon dioxide 1-53 1-53 1-60 
Sulphur dioxide ... 2-19 2-13 7:07 
Chloroform 4°32 488 319 
Methyl iodide 5:05 4-80 720 
Prof. Rutherford suggested some comparative experiments 
to ascertain if the more penetrating Rontgen rays, after 
passing through thick metal screens, were similar in their 
action to the y rays of radium. The experiments have 
proved that the relative conductivity imparted to gases by 
Rontgen rays is a function of the penetrating power of the 
rays employed, and the results obtained approximate to 
those found for the y rays rather than to the high figures 
previously quoted for Rontgen rays. 
In the experiments, two electroscopes were placed side by 
side, completely enclosed in two thin lead vessels the sides 
of which were 1-8 mm. thick. A large ‘‘ hard ”’ bulb and 
a powerful induction coil were used. The rates of dis- 
charge for air were ascertained to be identical, and one of 
the electroscopes was then filled with gas under examin- 
| ation, and the rates were again measured. 
| In the case of sulphuretted hydrogen, for which a ratio of 
| six to one has been obtained for ordinary Réntgen rays, the 
present experiments for penetrating rays showed a close 
equality with air. This is in agreement with the relative 
conductivity obtained for the y rays. Results of a similar 
character have been obtained for chlorine and for air 
saturated with chloroform. Further experiments are in 
progress to compare the relative conductivity of a number 
of gases for the two kinds of rays. 
The results so far obtained indicate that the differences in 
the relative conductivity of gases, previously observed for 
Rontgen and y rays, were due to the great difference in the 
penetrating power of the rays in the two cases, and that, for 
R6ntgen rays comparable in penetrating power with the 
y rays, these differences to a large extent disappear. 
ASS: JEViEs 
McGill University, Montreal, February 18. 
Nature of the y Rays from Radium. 
THE interesting results recorded by Mr. Eve in the pre- 
ceding letter on the relative conductivity of gases for very 
penetrating Réntgen rays removes the strongest objection 
that has been urged against the common belief that the 
y rays are an extremely penetrating type of Roéntgen rays. 
All the experimental evidence so far obtained is now in 
agreement with the view that the y rays are very pene- 
irating Rontgen rays which have their source in the atom 
of the radio-active substance at the moment of the expulsion 
of the B or kathodic particle. For example, I have found 
that the y rays from radium always accompany the B rays, 
and are always proportional in amount to them. In radium 
the 6B and y rays appear only in the third change occurring 
in the radio-active matter which causes ‘‘ excited activity,” 
i.e. in the fourth of the chain of radio-active products which 
result from the disintegration of the radium atom. 
In addition, as Mr. Ashworth pointed out in a recent letter 
to this Journal (January 28), the fact that the amount of 
y rays from radium is independent of its degree of concentra- 
tion points to the conclusion that the y rays arise from 
the disintegrated atom, and are not secondary rays set up 
by the bombardment of the radium as a whole by the 
| B rays. 
On the theory of the nature of Réntgen rays, developed 
