ON SEISMOLOGICAL INVESTIGATIONS. 217 
The President (Professor Turner) and Secretary (Professor Rothé) of the Seis- 
mological Section were re-elected (as was the case in most of the other Sections); and the 
subvention for seismology was increased, so that the printing of the summary can now 
be paid forout of International funds, though the computing is still otherwise provided. 
At the moment of completing this report, the sad news has been received from 
Madrid of the death of Senor Cubillo, who played a leading part in the hospitable 
reception in Spain. 
Instrumental. 
(From Notes supplied by Mr. J. J. Shaw.) 
As no results have been obtained from the seismograph taken to Christmas Island 
by the Eclipse observers in 1922, the return of the instrument has been requested, 
and promised by the General Manager of the Christmas Island Phosphate Company, 
Limited. 
During the year Mr. J. J. Shaw has supplied seismographs to Bidston Observatory 
(Birkenhead), Atherton Collieries (Lancs.), Adelaide (S. Australia), and a second 
component to Wellington (New Zealand), and to the Wembley Exhibition (R.S. 
exhibit). 
The Bidston Observatory is of special interest, both geologically and historically. 
Bidston Hill on which it stands is an outcrop of Kuyper Sandstone, altitude 180 feet, 
two miles from the sea, and the seismograph room is excavated in this rock. The 
stability of the foundation was recognised as early as 1896, when our Committee, 
then newly formed, resolved to place a Darwin Bifilar Pendulum in this vault. The 
Committee installed the first component in 1897 and the second in 1899. A Milne 
Seismograph was added in 1900, and in 1914 the Director (Mr. W. E. Plummer) 
secured the first constructed Milne-Shaw to replace the Milne. This instrument in 
turn has been replaced by a Milne-Shaw of modern pattern (greater scale), the former 
instrument being taken in exchange. It will be mounted at Oxford as a second 
component, but at present is on loan to the R.S. exhibit at Wembley. 
Taking advantage of the stability of the Bidston situation, and by way of experi- 
ment, the new Milne-Shaw has been given the high sensitivity of 66 mm. amplitude 
for one second of are tilt. An excellent series of seismograms obtained with this 
instrument points to a distinct improvement, and a similar arrangement was made at 
Dyce, Aberdeen, but on July 6 the amplitude shown at Dyce was only one-third of 
that at Bidston, where the foundation is gravel. Interpretation of this discrepancy 
is reserved until further records have been obtained. 
At Bidston, the effect of the tidal load of the sea (about two miles distant) is now 
much more marked, the traces opening and closing across the sheet ; apparently the 
sandstone yields about 0”.3 (of arc) between low and high water. 
The two components installed at the bottom of the Astley Colliery, 2,500 feet 
below the surface, have been purchased by the Lancashire and Cheshire Coal Research 
Association, with the object of determining whether any premonitory movements can 
be detected before the more important ruptures which occur from time to time. A 
number of records have been taken, including seismograms, but so far have not been 
discussed. 
Some experiments were made at West Bromwich to test the effect of high pendulum 
periods upon seismograms. Two machines were set to record the same component 
with the following constants— 
A. Magnification 250. Damping 20: 1. Pendulum period 25.2 sec. Tilt sensi- 
tivity 192 mm. amp. for | sec. of arc. 
B. Magnification and damping the same. Period 9.3 sec. Tilting sensitivity, 
27 mm. for 1 sec. of arc. 
A was roughly seven times more sensitive to tilting than B ; but much the same as 
regards magnification for rapid horizontal movement. 
The preliminary waves, the secondary waves, and the maximum phases were all 
increased in amplitude from 4 to 7 times on A as might have been expected, but the 
remarkable feature was, that the amplitude of the microseisms remained precisely 
the same from both machines. 
At first sight this would seem to indicate that microseisms are purely horizontal 
movements ; but, if so, it is not readily explained why they are recorded by a vertical 
component seismograph. The experiment also shows that a higher pendulum period 
is helpful in extricating earthquake waves from the mass of microseisms which often 
mask their appearance. 
