ON SElSMOLOGlCAL INVESTIGATIONS, 49 



lias beeli reached. This accounts for the fact which has so frequently 

 been confirmed by my own experiences that this type of instrument 

 fails to record very small movements. Why the second type of instru- 

 ment carries the same objection is not so clear. We frequently notice 

 that the traces from these instruments are not only broad, but they are 

 wanting in definition. Small movements may possibly be lost in the 

 ill-defined edges of the trace. 



On December 28, 1908, Messina and Eegio were ruined. Eight of 

 the after-shocks reached the Isle of Wight, but only two of these seem 

 to have been recorded at Laibach, Gottingen, and Hamburg, which are 

 nearer to the origin than the Isle of Wight. 



A similar story is told in all the registers published since 1907. 

 Earth messages appear to be passing beneath observatories all over 

 the world, but their existence is not recdgnised, because the instruments 

 generally used are not capable of recording the same. To exploit this 

 new department in seismology old types of instruments will have to be 

 improved or new ones adopted. 



V. Changes in Level accompanying certain Earthquakes. 



All geologists are familiar with the enormous mass displacements 

 which have accompanied very large earthquakes, particularly in the 

 vicinity of their origin. It does not, however, appear to have been re- 

 cognised that Small changes in level may sometimes be detected at great 

 distances from the same. Evidences of such changes are occasionally 

 to be seen in the records obtained from horizontal pendulums. As an 

 illustration of this I will refer to the earthquake of January 22, 1910, 

 which had its origin to the north of Iceland. With the maximum motion 

 of this disturbance at Shide, in the Isle of Wight, the booms of five 

 horizontal pendulums were suddenly displaced from their normal posi- 

 tion. Those oriented east and west were swung to the north, whilst 

 those at right angles to the west. Pendulums in rooms 80 yards apart 

 were displaced similarly. In their new positions they were all free 

 to swing. The displacement took place at 8 a.m., but at 12.45 they 

 crept back somewhat intermittently towards their original zero. This 

 they reached at 4 p.m. The behaviour of pendulums at Bidston and 

 West Bromwich suggested a displacement similar to that at Shide. In 

 the seismograms which I have accumulated during the last fifteen years 

 I find many repetitions of a similar phenomenon. 



VI. Changes in Level due to Tidal Influence. 



Towards the end of last year it occurred to Professor Milne that 

 the conditions under which the earthquake records were made at 

 Bidston might be utilised to determine the amount of deformation of 

 the earth's surface due to the accumulation and removal of a heavy 

 load of tidal water. 



A few years ago, in the basement of the Victoria Club at Eyde, 

 Professor Milne made some observations with this in view. Contrary to 

 expectations, it was found that when the tide rose the strand rose 



1910. b 



