NOVEMBER 6, 1913] 
great value, as all points of view were represented, 
and gave a much clearer notion of the trend of 
thought on this fundamental subject to those who 
have not been able to follow the literature very care- 
fully. We understand that the discussion is to be 
published in full in the reports. This will be a 
valuable addition to the literature of the subject. 
Sir Joseph Larmor gave a short account of a 
paper on lightning and protection from it. He dis- 
- cussed the relation of the field of force near a lightning 
conductor and the mechanism of the discharge. It 
was unfortunate that there was only a few minutes 
for the subject, as there was no discussion, and the 
views brought forward were of great practical im- 
portance. It is to be hoped the paper will appear in 
full and will have the attention it deserves. 
Prof. W. H. Bragg spoke on X-rays and crystals, 
which was of great interest and importance. The 
paper was discussed at a special meeting of the 
section on Tuesday afternoon. It was unfortunate 
that some of those most interested—Profs. Pope, 
Barlow, and Armstrong, for example—were unable 
to be present at the discussion. Prof. Bragg gave 
an account of the new method of tsing characteristic 
Réntgen rays and crystals. With his son, Mr. W. L. 
Bragg, he had obtained as many as five orders of 
spectra by reflection at certain planes of the 
crystals. If in a crystal there are planes 
specially rich in atoms, these planes, spaced 
at definite distances, act somewhat in the manner of 
an echelon grating, and spectra are produced. From 
the characters of the spectra of different orders— 
absence, diminished intensity, and so on—the spacing 
of the planes can be determined, and so we have a 
new method of determining the arrangement of atoms 
in crystals. The diamond has been thoroughly 
examined, and a model of its structure was shown. 
The method is a singularly beautiful one, and 
apparently not open to criticism. The method also 
provides, in the words of Prof. Bragg, a spectroscope 
for X-rays, and measurements could be made without 
doubt to an accuracy of 1 part in 1000. For the dis- 
cussion of the paper Prof. Bragg specially came back 
to Birmingham and gave further details of the 
method. Prof. Arrhenius congratulated the authors, 
and remarked that it was the beginning of a new 
crystallography. Reference was made to the work 
of Pope and Barlow, and Prof. Bragg explained that 
in his view the differences between the structures 
obtained by the new method and by the old might be 
reconciled. He made no claim to have contradicted 
the work resting on the theory of close packing. 
The paper and discussion were listened to by large 
audiences, and formed one of the most interesting 
parts of a successful meeting. 
On Friday, after the radiation discussion, the 
department of mathematics met separately, when 
two papers on mathematical physics were read. 
Prof. Eddington spoke on the dynamics of a globular 
stellar system. The problem attacked is that of the 
determination of different possible distributions of 
velocity which correspond to a steady state. In the 
paper a number of simpler cases are worked out. It 
is of special interest to find a system in which there 
is a strong preference for motion to and from the 
centre (following Prof. Turner’s suggestion for ex- 
lanation of the two star streams). Systems satisfy- 
ing this kind of motion, and also requiring only a 
finite density at the centre of the system, have been 
found. The other paper at this meeting was by Dr. 
Swann on the expression for the electrical conductivity 
of a metal deduced from the electron theory. 
On Monday the department of general physics held 
a joint discussion with Section G (engineering) on 
NO. 2297. VOL. 92] 
NATURE 397 
the investigation of complex stress distribution. This 
discussion was more on the engineering side than the 
physical, and will be dealt with in the special article 
on the proceedings in Section G. The department of 
cosmical physics met at the same time, and several 
important papers were contributed. Mr. C. Bag ste 
John, of Mount Wilson Observatory, gave an 
important account of some late results of solar work 
at Mount Wilson. He made out a clear connection 
between the radial velocity of gases in the solar 
atmosphere and the intensity of the lines which are 
used in the velocity determinations. That is to say, 
a connection has been demonstrated between radial 
velocity and the level in the solar atmosphere. The 
displacements of Fraunhofer lines in the penumbre 
of sun-spots thus is shown to give a means of 
sounding the solar atmosphere and of assigning 
relative levels to the sources of the lines. The results 
obtained clearly open a wide field for further solar 
research. 
Dr. S. Chapman gave an interesting paper on the 
lunar influence on terrestrial magnetism and _ its 
dependence on solar periodicity. On Schuster’s 
theory of the variation of magnetic force Dr. Chap- 
man considered the effect of the lunar tide in the 
earth’s atmosphere. This effect can be detected in 
the observations. The solar effect is due to the 
ionisation and conductivity in the upper atmosphere 
depending on the sun’s hour angle. The study of 
the lunar period is valuable, as it enables us to 
separate the two effects, periodicity in the atmosphere 
and periodicity in the conductivity. No apparent 
relation has been detected between the conductivity 
and the eleven-year solar cycle. A paper on solar and 
terrestrial magnetic disturbances was read by the 
Rev. A. L. Cortie, S.J. 
Two interesting papers on meteorology were read— 
Mr. J. I. Craig on a temperature see-saw between 
England and Egypt, and on temperature frequency 
curves by Mr. Gold and Mr. F. J. W. Whipple. 
There were two papers on seismology: ‘The Dis- 
tribution of Earthquakes in Space and Time,”’ by the 
Rev. H. V. Gill, S.J.; and ‘‘Notes on the Construc- 
tion of Seismometers,”’ by the Rev. W. O’Leary, S.J. 
A communication of general interest was read by Dr. 
J. S. Owens, deaiing with methods for measuring 
the amount of atmospheric pollution by suspended 
matter, such as smoke and dust. Prof. H. H. 
Turner gave a paper on the Fourier sequence as a 
substitute for the periodogram. Mr. J. H. Reynolds’s 
communication on arrangements for a reflecting tele- 
scope was taken as read. After the joint discussion, 
the department of general physics met for another 
important session. Prof. Pringsheim gave his paper 
on a theory of luminescence and the relation between 
luminescence and pure temperature radiation. It was 
interesting to the section to hear in Prof. Pringsheim 
another distinguished foreign visitor, and one whose 
name is intimately connected with the experimental 
results that form the foundation of the new theories 
of radiation. 
The next paper was by Prof. R. W. Wood, of 
Baltimore, who is well known as one of the most 
brilliant experimentalists of our day. He described 
some experiments on resonance spectra under high 
dispersion. As is expected of Prof. Wood, most 
interesting and amusing details of experiments were 
related. The method of removing spider-webs from 
the long buried tube of the spectrograph by sending 
“the household pussy cat” through is an original 
and effective method of attaining the desired end. 
Amongst the many interesting details of the work, 
which will be fully described elsewhere, may be men- 
tioned the method of exciting the resonance spectrum 
