130 REPORT— 1897. 



and there were strong reasons for believing that we might expect assist- 

 ance from both the Royal Geographical and Eoyal Astronomical Societies. 



Letter sent to various Observatories and Persons. 



Bbitish Association for the Advancement of Scibncb : 



Burlington House, 



London, W. 



1897. 



To ' 



giB^ — It has been established that the movements resulting from a 

 large earthquake originating in any one portion of our globe can, with 

 the aid of suitable instruments, be recorded at any other portion of the 

 same ; therefore the Seismological Investigation Committee of the 

 British Association are desirous of your co-operation in an endeavour 

 to extend and systematise the observation of such disturbances. 



Similar instruments should be used at all stations ; and the one 

 recommended by this Committee as being simple to work, and one that 

 furnishes results sufficiently accurate for the main objects in view, is 

 indicated in the accompanying report (see pp. 2-4) by the letter M ; a 

 sketch of the same is shown on p. 7, whilst there is an example of one of 

 its records on p. 49. 



We desire to know whether you are disposed to purchase, and make 

 observations with, one of these instruments, the cost of which, including 

 photographic material to last one year, packed for shipment, is about 50Z. 

 Should you reply in the affirmative, we shall be pleased to arrange with 

 a competent maker for the construction of an instrument for you, and to 

 furnish instructions respecting installation and working. In case an 

 instrument be established at your observatory, we should ask that notes 

 of disturbances having an earthquake character be sent to us for analysis 

 and comparison with the records from other stations. From time to time 

 the results of these examinations would be forwarded to your observatory. 



The first object we have in view is to determine the velocity with 

 which motion is propagated round or possibly through our earth. To 

 attain this, all that we require from a given station are the times at 

 which various phases of motion are recorded ; for which purpose, for the 

 present at least, we consider an instrument recording a single component 

 of horizontal motion to be sufficient. Other results which may be ob- 

 tained from the proposed observations are numerous. 



The foci of submarine disturbances, such, for example, as those which 

 from time to time have interfered with telegraph-cables, may possibly be 

 determined, and new light thrown upon changes taking place in ocean beds. 



The records throw light upon certain classes of disturbances now and 

 then noted in magnetometers and other instruments susceptible to slight 

 movements ; whilst local changes of level, some of which may have a 

 diurnal character, may, under certain conditions, become apparent. 



Trusting that you will find it possible to co-operate in this endeavour 

 to extend our knowledge of the earth on which we live, 

 We remain, Sir (on behalf of the Committee), 



Your obedient servants, 



G. J. SYMONS, Chairman, C. DAVISON, "I Jbmi iTonorary 



J. MILNE, J Secretaries. 



