GENERAL MEETINGS. 17 
305tH MEETING. OcToBER 15, 1887. 
The President in the Chair. 
Fifty-one members and guests present. 
The President announced the death at Wood’s Holl, Massachu- 
setts, on August 19, 1887, of Prof. Spencer FuLLertTon Barrp, 
one of the original members of the Society. 
Mr. C. E. Durron made a communication 
ON THE DEPTH OF EARTHQUAKE FOCI. 
[Abstract. ] 
Mr. Dutton first referred to the various methods which had been 
resorted to in order to ascertain the depths of earthquake foci. The 
method suggested by Mallet and based on the assumption that the 
lines of fracture in the walls of buildings tended to arrange them- 
selves transversely to the direction of propagation, he believed to be 
unavailable and not sustained by observation. The motions of 
buildings ‘and of the ground itself during an earthquake were 
highly complex, and, moreover, the lines of fracture, he believed, 
were influenced far more forcibly by the nature of the structure, 
the openings in the walls, and the natural directions of vibration 
than by the directions of the impulses themselves. 
Seebach’s method, by ascertaining the variation of the speed of 
the wave along the surface of the ground in the vicinity of the epi- 
centrum, was regarded as impracticable, though the mathematical 
considerations upon which it was founded were doubtless correct. 
The speed of propagation is so high and the difficulty of obtaining 
time observations of sufficient precision is so great that this mode 
of solution must fail for want of the requisite data. Seebach seems 
to have been under the impression that this speed was not more 
than a very few hundred metres per second. The Charleston earth- 
quake was transmitted with a speed probably exceeding 5,000 metres 
per second, and Mr. Dutton was of the opinion that all true earth- 
quakes were propagated with a speed differing but little from that ; 
but, even if the speed were no greater than Seebach supposed, it 
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