+ 
~ Aprit 1 4, 1923] 





































- Societies and Academies. 
Lonpon. 
_ Zoological Society, March 20.—Prof. E. W. 
MacBride, vice-president, in the chair—S. Ch. 
Sarkar: A com tive study of the buccal glands 
and teeth of Seelam snakes, and a discussion 
on the evolution of the order from Aglypha.— 
Oldfield Thomas and M. A. C. Hinton: On the 
mammals obtained in Darfur by the Lynes-Lowe 
dition—R. I. Pocock: (1) On the external 
Cc) ters of Elaphus, Hydropotes, Pudu, and other 
Cervide. (2) The classification of the Sciuride. 
_ The Optical Society, March 22.—Instr.-Commander 
T. Y. Baker in the chair.—Dr. L. C. Martin: Survey- 
g and navigational instruments from a historical 
int. Before a.p. 150 accurate knowledge of 
editerranean basin was obtained by Ptolemy. 
One of the best known of the early instruments was 
the astrolabe, and this instrument was developed 
iderably by the Arabs and others. Specialised 
were used for navigation. In the seventeenth 
century a simplified form of the astrolabe, capable 
of being suspended or mounted horizontally on a 
tand, was employed as a theodolite. This was 
ubsequent to the description of Digges’s theodolitus, 
in which independent horizontal and vertical axes 
were employed. The use of the telescopic sight was 
not applied to surveying instruments till the beginning 
of the eighteenth century. The history of the level, 
from the “ open sight and gravity controlled ”’ forms 
to the telescopic levels of Picard and the bubbles 
of Thévenot, was also discussed. Improvements by 
various artists in the methods of graduation of circles 
and the development of dividing engines from 
Hindley to Ramsden and Troughton were matters 
of the greatest moment in the development of modern 
instruments. Later developments were shown in 
the instruments by Troughton and by Cary, which 
brought the level of construction (from the purely 
scientific point of view) almost up to that of our 
own time. 
tang 
forms 
CAMBRIDGE. 
Philosophical Society, March 5.—Mr. C. T. Heycock, 
president, in the chair.—Sir Ernest Rutherford: The 
capture and loss of electrons by a-particles. In a 
recent etd (Proc. Roy. Soc: A, 102, p. 497, 1922) 
G. H. Henderson showed that swift a-particles can 
pture electrons and are thus converted into singly 
charged and neutral helium atoms. The magnetic 
deflexion of a pencil of a-rays in a high vacuum 
showed by the photographic method after passing 
mica the presence of two bands—one, the 
d, due to He + +, and the other, the midway 
nd, due to He +particles. The relative number of 
_ the latter increased rapidly with reduction of velocity 
ofthe a-rays. These conclusions have been confirmed 
_ by the scintillation method. By deflecting the mid- 
way band by a combined electric and magnetic field, 
it has been proved that it is due to He + particles. 
For any velocity there is a temporary equilibrium 
_ between the number of He + + and He+ particles, 
_ such that the number of captures is equal to the 
_ number of losses. The ratio of the numbers of singly 
and doubly charged particles between the velocities 
7:7 x 10° and 18 x 10° cm. per second, varies approxi- 
mately as the inverse fifth power of the velocity. 
The disappearance of the midway band when gas at 
low pressure is introduced in the path of the rays 
_ gives a method of determining the mean free path of 
q NO. 2789, VOL. 111] 
4 
? 
thro 
NATURE 
519 
the He + particles in air and other gases before con- 
version into He+ +. The mean free path varies 
roughly as the velocity of the a-rays, and is 4 to 5 
times longer in hydrogen and helium than in air. 
The mean free ate for capture varies roughly as the 
inverse sixth power of the velocity. The mean free 
path in air for a velocity 1-5 x10*® cm. per sec. is 
about 0-56 mm. at N.T.P. for capture and 0-008 mm. 
for loss. The average a-particle captures and loses 
an electron many hundred times before it is absorbed. 
—P. Kapitza: Some observations on a-particle 
tracks in a magnetic field —H. Lamb: The magnetic 
field of a helix—W. Burnside: (1) The theory of 
errors of observation ; (2) The solution of a certain 
partial difference equation.—P. M. S. Blackett: A 
note on the natural curvature of a-ray tracks. 
An apparent relation exists between the plane and 
direction of the curvature of the parts of a forked 
track and the plane and type of the fork itself. The 
natural curvature possibly involves the effect on the 
ionisation of the probable assymmetric structure of 
singly charged a-particles. 
SHEFFIELD. 
Society of Glass Technology (Birmingham meeting), 
March 21.—Prof. W. E. S. Turner in the chair.— 
H. S. Blackmore, Violet Dimbleby, and W. E. S. 
Turner: A rapid method of testing the durability of 
glassware. When a very dilute solution of 1 part in 
1000 of the alkaloid, narcotine hydrochloride, is 
heated to boiling-point inside a glass vessel, the alkaloid 
is thrown out of solution, and can be seen as a fine 
precipitate if the glass is of poor quality. Good 
glasses should show no sign of deposit when heated 
at the boiling-point for an hour.—D. Turner and 
W.E.S. Turner: The corrosion of fireclay refractory 
material by glass and glass-making materials.— 
Edith M. Firth, F. W. Hodkin, and W. E. S. Turner : 
The effect of saltcake in corroding fireclay materials. 
Both papers were presented by Prof. Turner. Ex- 
perimental evidence was detailed, showing that in 
glass-melting the corrosion of the pots or the tank 
blocks is most severe during the early stages of the 
melting of the batch; sodium nitrate, potassium 
nitrate, and borax are particularly corrosive. As the 
proportion of saltcake used in the batch increased, so 
did the extensiveness of the corrosion. Resistance 
to corrosion can be improved by firing the pots and 
blocks at 1400° C. before the charge of batch was 
inserted 
Paris. 
Academy of Sciences, March 19.—M. Albin Haller 
in the chair.—The president announced the death 
of M. Van der Waals, foreign associate.—Emile 
Borel: The approximation of rational or incom- 
mensurable numbers belonging to given enumerable 
ensembles.—L. Lecornu: The time of revolution 
of the planets. A discussion of a question raised 
in a recent note by M. Jean Chazy.—Charles Moureu 
and Charles Dufraisse: Auto-oxidation and anti- 
oxygenic action. The catalytic properties of iodine 
and its compounds. The case ofacrolein. According 
to the theory of the mechanism of anti-oxygenising 
action developed by the authors, iodine and its 
compounds should exert catalytic properties in 
phenomena of auto-oxidation, and should, under 
certain conditions, possess the anti-oxygenising pro- 
perty. lIodides of various metals and organic bases 
(33 in all) were shown to inhibit the oxidation of 
acrolein at a concentration of 1 in t000.—IL. Maquenne: 
The hydrolysis of maltose by malt extract.—G. 
Gouy: The improvement of the microscope by the 
