ON SEISMOLOGICAL INVESTIGATION. 75 



Inasmuch as the instruments with the least sensibility might fail in 

 recording certain very small earthquakes which might disturb an instru- 

 ment with a higher sensibility, and that the instruments with the lower 

 sensibility would not move so long or be displaced so far whether the 

 motion was horizontal or angular, as would be the case with instruments 

 the booms of which were more easily displaced, it appears that what has 

 been recorded finds its best explanation in the assumption that the same 

 is due to difl'erences in the sensibilities of the apparatus employed. 



If we assume that the amplitudes given in millimetres are quantities 

 to be represented in angular measure, then the displacements at the four 

 stations may be stated as follows : — 



Kew, 32"-l ; Edinburgh, 28"-4 ; Shide, 27"-4 ; Bidston, 19"-0. 



One inference from this is that the installations at which it was first 

 supposed there was the feeblest seismic sensibility are those at which it 

 is most marked. 



Observations are now being made at these four stations with the 

 instruments so adjusted that a 4° turn of the calibrating screw results in 

 a deflection at the outer end of the pendulum of 14 mm., which means 

 that they have equal sensibilities to tilting although their periods may 

 differ (see p. 60). 



XII. An Attempt to Detect and Measure any Relative Movement of the 

 Strata that may now he taking j?lace at the Ridgeway Faidt, near 

 Upway, Dorsetshire. Third Report by Horace Darwin, August 1902. 



In the last Report a hope was expressed that the alterations made in 

 the apparatus had prevented the water getting into the oil vessels ; this 

 has not been the case, water again having blocked the pipes connecting 

 them. It is probable that water enters in the form of vapour and con- 

 denses, and as we saw no way of preventing this we decided to replace 

 the oil by a saturated solution of common salt ; an overflow was arranged, 

 and it is hoped that there will be no more trouble from this cause. It 

 was also discovered that the pipe connecting the vessels was not quite 

 straight, and that slight undulations in it prevented the free flow of the 

 liquid ; this is being rectified. 



Magnetic Observations at Falmouth. — Beport of the Committee, con- 

 sisting of Sir W. H. Preece (Chairman), Dr. R. T. Glazebrook 

 (Secretary), Professor W. G. Adams, Captain Creak, Mr. W. L. 

 Fox, Professor A. Schuster, and Sir A. W. Rucker, appointed 

 to co-operate with the Committee of the Falmouth Observatory in 

 their Magnetic Observations. 



The Committee report that the grant voted at the last meeting of the 

 Association has been used in support of the ordinary magnetic work of 

 the Falmouth Observatory, and that records of the horizontal force and 

 declination have been kept during ten years. The curves up to the end 

 of 1901 have been examined at Kew, and the results are of real value. 

 The vertical force instrument has been a cause of some difficulty ; the 

 examination of the 1901 curves led Dr. Chree to suspect the existence of 



