264 REPORTS ON THE STATE OF SCIENCE, ETC. 



Seismographs. 



The six Milne-Shaw seismographs belonging to the British Association 

 have remained on loan to the seismological stations at Oxford (2), Edinburgh, 

 Perth (W. Australia), and Cape Town (2). 



During the year a Jaggar shock recorder has been made for the Com- 

 mittee at Bristol under the supervision of Dr. C. F. Powell. This instru- 

 ment is to be set up at Dunira, near Comrie, the village in Perthshire 

 which is famous for the prolonged series of minor earthquakes in the last 

 century. It may be recalled that a Committee appointed by the British 

 Association set up seismometers, in Comrie and near by, with which to 

 measure the amplitude of earthquake waves. Eight of the seismometers 

 were inverted pendulums, designed by Prof. J. D. Forbes and ' working 

 on the principle of the watchmaker's noddy.' These instruments were 

 affected by the local earthquakes on two or three occasions, but they were 

 not sensitive enough to be disturbed by the majority of the shocks. After 

 an interval from 1844 to 1867 the Committee for registering earthquakes 

 in Scotland was reappointed. Only one of the original seismometers was 

 then in use, the 10 ft. inverted pendulum in the church tower at Comrie. 

 The Committee decided to adopt a suggestion of Mallet's and provide a set 

 of small cylinders which were to topple over when an earthquake occurred. 

 A special hut, which still stands in the grounds of ' Dunearn,' was allotted 

 to the cylinders, but it is believed that no earthquake ever bowled them 

 over. As far as is known none of these primitive seismometers survives 

 in Perthshire, but there is in the Royal Scottish Museum at Edinburgh 

 one of Forbes 's inverted pendulums. It is hoped that the new shock recorder 

 will eventually provide some evidence as to the nature of the earth-move- 

 ments in the Comrie region. The Committee is indebted to Mr. W. G. 

 Macbeth of Dunira for allowing the installation of the instrument, and to 

 Mr. White who is undertaking to operate it. 



Geocentric Co-ordinates. 



Owing to the progress in the precision of seismological observations, 

 and in the accuracy of the tables with which the observations can be com- 

 pared, it has now become desirable to take into account the ellipticity of 

 the earth, both in locating the epicentres of earthquakes and in discussing 

 the behaviour of seismic waves of different types. It was pointed out by 

 Gutenberg and Richter, in 1933, that this could be done most readily by 

 using geocentric co-ordinates instead of the ordinary geographical co- 

 ordinates. Investigations by Dr. Jeffreys and by Dr. Bullen have confirmed 

 the desirability of this refinement. Tables giving for each observatory 

 rectangular co-ordinates on the new system, or rather the direction cosines 

 of the radius from the centre of the earth, are required. The Committee 

 enlisted the help of Dr. L. J. Comrie, who has had the necessary calculations 

 made and is seeing the resulting tables through the press. These tables 

 will be published in the autumn. 



Geographical angular distances have been employed hitherto in the 

 International Seismological Summary, as in almost all other work on 

 earthquakes ; i.e. the angle between the verticals has been regarded as 

 giving the distance between two points on the globe. A method of utilising 

 the data without recomputing the distances ab initio has been devised by 

 Dr. Bullen. Tables computed by Dr. Bullen for use in the application' of 

 this method have been published by the Committee, with an Introduction 

 by Dr. Jeffreys. 



