284 REPORTS ON THE STATE OF SCIENCE, ETC. 
Instrumental. 
‘he Milne-Shaw seismograph in the basement of the Clarendon Laboratory 
at Oxford has worked well throughout the year. It is one of the early machines 
of this pattern, and the scale is smaller than that on more recent machines. 
The question of replacing it by one with a more open scale has been con- 
sidered, but it is thought better at present to supply the improved pattern to 
distant stations, from which there has been a succession of demands sufficient 
to keep Mr. Shaw closely at work. 
During the year he has dispatched machines to Ottawa (2nd component), 
Hong Kong (2nd component), Strasbourg, Hyderabad, Perth (W.A.), and Stony- 
hurst. Of these only that for Perth is the property of the B.A. Committee, 
and represents a loan (again owing to the generosity of Dr. J. E. Crombie) ; the 
others are all purchases. But they are mentioned here to show the distribution 
of machines of the type which is essentially the product of this Committee ; 
for Mr. Shaw began his experiments at the request of John Milne. 
It was mentioned in the last Report that a machine had been taken 
to Christmas Island by the eclipse observers from the Royal Observatory, 
Greenwich. An accident to the time-clock on the voyage led to considerable 
delay in setting up the instrument, which was only erected just before the 
observers left, after the eclipse, for home. It was expected that records would 
have been received before this, but nothing has yet come, and Mr. Jones is 
kindly making inquiries into the matter. 
Mr. Claxton has kindly sent to Oxford for examination most of the Hong Kong 
films which contain earthquake records, and they are naturally of great interest to 
us as showing the effects of disturbance at distances so much smaller than those to 
which we are accustomed. The record for March 24 last is specially noteworthy. 
The earthquake was very destructive in a region (32° N. 102° E.) not far from 
the destructive earthquake of December 16, 1920 (35°.5 N. 105°.5 E.). 
Bulletins and Tables. 
The Bulletins to the end of the year 1917 have been printed and distributed. 
The title of the publication was then changed, as above mentioned, to ‘ The 
International Seismological Summary,’ the first number of which contains the 
results from January to March, 1918; the next number, April to June, 1918, is 
passed for press; July to November, 1918, is ready in manuscript, though some 
checking of the later months is still required. The work steadily increases 
owing to the communication of results from new stations, and the receipt of 
arrears from older ones. 
The Tables for P and S have been expanded to give results for every tenth 
of a degree, and will be distributed with the next number of the Summary. 
This expansion has been delayed in the hope of first obtaining corrections of the 
tables, but it becomes clear that this may take some time owing to the compli- 
cation introduced by consideration of focal depth, and in any case the present 
tables will be applicable to a great deal of work already in print. 
Depth of Focus. 
It was mentioned in the last Report that the time of arrival of the earliest 
disturbance at the opposite side of the earth gives valuable indication of the 
depth of focus. The number of instances then available was small, but several 
more have been found during the past year, and successfully treated by the 
provisional formule then given. As they are fully dealt with in the Bulletins 
and Summaries there is no need to reproduce them here, but new light has been 
thrown on the possibilities by a paper by the late Prince Galitzin, dated 1919 
but only recently received from Petrograd. From a study of the angles of 
emergence he was led to infer three critical surfaces at depths 106, 232, and 492 
kilometres below the earth’s surface: or 0.017, 0.036, 0.077 in terms of the 
earth’s radius. ‘This work is quite independent of the investigation of focal 
