ON SEISMOLOGICAL INVESTIGATIONS. 55 



magnetic damping, and if he is successful it is proposed to order an 

 instrument from liim for use at Shide. Itwill be especially useful (1) in 

 showing when there has or has not been an earthquake, for guidance 

 in changing the paper of the photographic machines, and (2) for showing 

 to the numerous visitors to Shide the working of a seismograph without 

 disturbance of the photographic machines. In both respects it will 

 replace the large ' lamp-post ' machine formerly set up by Milne, but 

 discontinued as too cumbersome. 



Time Signal at Shide. — On the outbreak of war, the wireless apparatus 

 used for receiving the time signal from the Eiffel Tower was dismounted 

 in accordance with instructions from the Post Office, and for some months 

 it was difficult to obtain correct time. In December 1914 a small 

 transit instrument, lent by the Royal Astronomical Society, was set 

 up on a disused seismograph pillar near the south window and adjusted 

 as well as possible with a view restricted to altitudes less than 45°. With 

 the kind help of a few telephone exchanges from the Royal Observatory, 

 Greenwich, this sufficed to give clock errors until May" 1915, when the 

 Post Office permitted the re-erection of the wireless apparatus. From 

 May 20 this has accordingly been in use again, and has confirmed the 

 accuracy of the transit determinations. On July 23 a storm blew down 

 the aerial, but it was re-erected next day. 



While the apparatus was dismounted and clock error being found 

 by the small transit, Mr. J. J. Shaw visited Shide for regulation of his 

 seismograph, and incidentally compared the Shide clock with his watch, 

 of which he knew the error and rate. To his surprise a large discrepancy 

 developed between the two, and it became clear that the watch was at 

 fault. The cause was traced to the suspension of the watch during the 

 night, which allowed of its vibrating as a pendulum. Attention was 

 drawn to this matter by Lord Kelvin many years ago, but the magnitude 

 of the possible error has scarcely been realised sufficiently. Mr. Shaw 

 recalled attention to the matter, which is of considerable practical im- 

 portance, in a short paper to the Royal Astronomical Society (' Mon. 

 Not.' Ixxv., p. 583). 



III. Seismic Activity in 1911, 1912, and 1913. 



Milne carried the list of origins to the end of 1910. From the be- 

 ginning of 1914 the origins of the larger earthquakes have been specified 

 in the monthly bulletins, at first adopted from the Pulkovo determina- 

 tions, and later, when it became clear that these could often be profitably 

 corrected," adopted from special determinations made at Shide. The 

 corrections are partly due to errors of the tables, estimated approximately 

 at the end of the last Report, but still under revision. It seemed desirable 

 to await these corrections to the tables before undertaking the com- 

 putation of origins for 1911-13 ; but these will shortly be commenced. 



IV. Distribution of Milne's Epicentre^!, 1899-1910. 



In the last Report a map of the world was given on an octahedral 

 projection, the precise selection of which had been suggested by the 

 study of the epicentres tabulated by Milne for the years 1899-1910. The 

 work of plotting the individual epicentres on this map had not then been 

 completed. When complete (as shown in the acompanying illustra- 

 tion) it showed that the root-idea of the map did not fit the facts in its 



