308 
NATURE 
of iodine by monochromatic illumination filtered 
through bromine vapour to supply light of a small 
enough range of wave-length to include only one line 
of the iodine spectrum. The paper was full of the 
kind of experimental perfection that is to be found in 
so much of Prof. Wood’s work. 
Prof. S. B. Maclaren gave a paper on a theory of 
magnets. This paper dealt with some of the difficul- 
ties of magnetic theory, and pointed out how an 
explanation of paramagnetism and diamagnetism may 
be arrived at. Magnetic induction is explained by 
means of tensions in the field acting on matter, and 
the molecular magnetic field is not explained as due 
to the circulation of electric current sheets. Prof. 
Coker gave a demonstration of large polarising 
apparatus for lantern projection. Beautiful pictures 
result, but the apparatus has been described before, 
and there is no need for details in this place. 
In the middle of the same morning the department 
of pure mathematics met, when communications were 
read by Prof. J. C. Fields, Prof. Hilton, Lieut.-Col. 
Allan Cunningham, Prof. A. C. Dixon, and Mr. 
M. D. Hersey. A paper by Prof. A. W. Conway was 
taken as read. 
On Tuesday morning there was a joint meeting 
with Section E (geography), when four papers on 
geodetic subjects were read. An account of this joint 
meeting will appear in the article describing the 
work of the geographical section, which will shortly 
be published in Nature. At the same time the 
department of general physics met and had another 
‘series of important papers and discussions. Dr. 
W. H. Eccles read an account of some experiments on 
contacts between electrical conductors. The paper 
explained the absence of a linear relation between 
current and electromotive force when the current 
passes across a ‘loose contact.” The behaviour of 
the contact was explained by purely thermal actions 
in the matter near the point of contact. The Joule, 
Peltier, and Thomson effects all play a part. 
Prof. Poynting read a paper on the twisting of 
indiarubber. By means of an exceedingly delicate 
piece of apparatus he had measured the changes in 
length and cross section of steel and copper wires 
under torsion, and had tried the same with india- 
rubber. Indiarubber showed no observable change in 
volume when twisted, but a very large increase in 
length when compared with steel. Sir J. J. Thomson, 
in discussing the subject, suggested a connection in 
the behaviour of these materials under magnetic 
influence. 
Two papers—one by Sir J. J. Thomson on X, and 
the evolution of helium, the other by Mr. F. W. 
Aston on a new elementary constituent of the atmo- 
sphere—created great interest. A number of chemists 
came to hear of this fresh invasion of their territory 
by Sir J. J. Thomson. The gas X,, which has been 
described before, is now considered by Sir J. J. 
Thomson to be H,. Evidence was given in the paper 
which though in detail perhaps not convincing, yet 
has great cumulative weight. The chemists present 
were prepared to accept the possibility of an H, 
molecule. As to the evolution of helium, there seems 
little doubt that it comes from the material bombarded 
by the kathode rays in the tube. Here there is a 
divergence between the views recently put forth that 
such helium results from a transformation of the gas 
in the discharge tube. In the discussion Sir Oliver 
Lodge emphasised the importance of these experi- 
ments, as in his opinion it was the first case of 
the artificial production of atomic disintegration. 
Mr. Aston dealt with an investigation of the 
existence of an element with atomic weight about 
22. Sir J. J. Thomson’s positive ray method 
NO. 2297, VOL. 92] 
had detected such an element, and the 
was an account of the partial separation of 
into two gases of approximate atomic wei 
199 and 22'1. The method was one of diff 
attested by a change of density. The method of d 
mining the density was by means of a specially c 
structed quartz balance of small size hung inside 
tube containing the gas. By adjustment of the 
pressure the quartz beam could be balanced and th 
density of the gas determined with great accuracy. 
The smallness and compactness of the apparatus 
enabled very small quantities of gases to be dealt 
with. No physical differences except in density ha 
been discovered between the two gases. 
Dr. E. E. Fournier D’Albe gave an account of the 
minimum quantity of light discoverable by selenium. — 
Very faint illuminations can be detected, and it was 
suggested that there might be a possibility of direct 
measurement of the Planck quantum of energy. A 
paper by Mr. H. B. Keene on the transmission of — 
X-rays through metals was of interest, especially as 
it was allied to Prof. Bragg’s paper on X-rays and 
crystals. Other papers were by Mr. F. Forrest 
on the electric arc ‘as a standard of light, and by Dr. 
G. A. Shakespear on the resistance of air to falling 
spheres and on a method of increasing the sensitive-_ 
ness of measuring instruments. The method was to — 
throw the image of a Nernst filament lamp from the 
mirror of any deflected instrument on to a radio- 
micrometer strip; any change in the direction of the 
original reflected beam of very small amount results 
in a large deflection of the radio-micrometer. The 
method can be repeated, and any increase in sensi- — 
tiveness obtained except for the difficulty of keeping — 
steady conditions. Mr. J. S. Anderson described a 
new method of starting mercury lamps. Papers by — 
Mr. W. H. F. Murdoch on a magnetic susceptibility 
meter, Mr. A. J. Lotka on a new process for en- 
larging photographs, and Prof. H. Stansfield on the 
sensitiveness of the human skin as a detector of low- 
voltage alternating electrostatic fields were taken as 
read. The discussion on Tuesday afternoon of Prof. 
Bragg’s paper has already been referred to. 
On Wednesday the first business was the presenta- 
tion of reports. On the report of the Seismological 
Committee Prof. Turner spoke of the loss to seismo- | 
logy and science generally in the death of Prof. John © 
Milne. The work of British seismology and seismo- — 
logy generally owes nearly everything to Milne; as a 
resolution of the committee expressed it, he may be 
said to have created a new science. For many years — 
past he had himself presented the annual report of © 
the Seismological Committee, and the report presented 
by Prof. Turner had been drawn up by him just before ~ 
his death. 
After the reports, papers were read by Mr. J. S. 
Anderson on a new method of sealing electrical con- 
ductors through glass, and by Mr. J. J. Shaw on a 
seismograph. This instrument had been exhibited 
during the meeting, and was of the Milne type, with 
its natural oscillations damped by means of an 
aluminium strip attached to the boom swinging 
between the poles of magnets. The instrument is of 
importance, and had a further interest in the fact that 
it was designed and constructed with the cooperation ~ 
of Prof. Milne just before his death. Papers by Dr. 
Vaughan Cornish on a method of determining the 
period of waves at sea, by Mr. Lotka on the dynamics 
of evolution, by Mr. Hookham on microscope crystals 
with epidiascope illustrations, and by Prof. T. R. 
Lyle on the Goldschmidt dynamo were taken as read. 
It was unfortunate that Dr. Vaughan Cornish, owing 
to a misunderstanding, arrived just after the sec- 
tional meeting was formally closed, but an informal 
