126 NOTES ON THE CONFERENCE OF DELEGATES OF THE 



the Secretary to the B. A. Committee deahng with this 

 subject, said that he would be glad to receive photographs show- 

 ing lightning flashes of an abnormal character. He added that he 

 read now and then in the newspapers accounts of the remarkable 

 effects produced by a whirlwind in this or that district. But he 

 usually found that it was then too late to have the results 

 photographed, the damage done having been repaired, or the 

 damaged object removed. In such cases he would be very grateful 

 to the Secretary of any local society in the district affected who 

 would get photographs taken at once and send them to him. 



Earth tremors. — Mr. Davison, Secretary of the Earth Tremors 

 Committee, gave some account of the work of the Committee, and 

 Mr. Horace Darwin described the construction and use of the 

 Bifilar Pendulum, which he has invented, and a full account of 

 which appeared in "Nature" of July 12th, 1894. He said it was 

 not affected by the rapid complicated movements which took place 

 during an earthquake, nor by the slight tremors produced by pass- 

 ing carts or trains. The movements which it would measure and 

 register were such as would make a factory chimney lean over to one 

 side. Extremely small movements of this kind could be detected. 

 Mr. Symons, the Chairman of the Earth Tremors Committee,, said 

 that some time ago the attention of the Committee had been directed 

 to certain vibrations recorded by an instrument placed at the bottom 

 of a deep mine in the district of Newcastle-on-Tyne. These pulsa- 

 tions were traced to two causes, one, the gradual settlement of the 

 ground in consequence of the removal of the coal, the other, the 

 beating of the waves upon the coast. Mr. Davison on one occasion 

 found pulsations were taking place which eventually turned out to 

 have been produced by an earthquake then going on in Cireece. 

 They wanted information, added Mr. Symons, as to the changes 

 going on in connection with the faults in geological strata, and, if 

 possible, to get records of the alterations in the earth's crust caused 

 by tidal waves. The Committee had one instrument under the 

 charge of Mr. Davison at Birmingham, but they wished to establish 

 others in various parts of the British Isles. 



In Essex we have no great lines of fault along the course ol 

 which an instrument for recording earth tremors would be especiall) 

 desirable. But in the small compact area from Colchester tc 

 Mersea, which was so severely damaged by the earthquake of 1884. 

 we have a tract of country in which we might expect earth trenion 



