140 



Dr. G. Gore. On the 



[Dec, 8, 



the direction of motion in the line joining the centre of disturbance 

 and the point of observation, while the other set has the direction of 

 motion at right angles to that line. The first of these is denominated 

 the direct wave, and the second the transverse wave. The direct 

 wave has a greater amplitude and a slightly shorter period of motion 

 at the source, but seems to die out more rapidly than the transverse 

 wave. The amplitude of the direct vibrations seems never to have 

 exceeded 0'5 millim. at 50 feet, and 0*1 millim. at 250 feet from 

 the centre. The amplitude of vibration was very nearly inversely 

 as the distance from the source. The direct wave was completely 

 cut off by the pond and nearly, if not completely, by the hill, 

 but the transverse wave extended along the distant side of the pond 

 to a considerable distance, and was little affected by tbe hill. When 

 the motion of a point on the earth's surface was registered by 

 means of a seismograph, it was found to be such as would result from 

 the composition of two harmonic motions of different period, and in 

 different directions. One of the most important points attended to in 

 these experiments was the determination of the velocity of propaga- 

 tion for the different waves. The method finally adopted for this 

 purpose was to mark by means of a telegraphic arrangement, simul- 

 taneously, and at definite intervals, on two smoked glass plates, placed 

 at different distances along the same line from the source, the same 

 instant of time. These plates were moved by clockwork, and were 

 used for the reception of the seismograph record. 



It is evident that the time-marks on the plate give the means of 

 comparing the times of arrival of the direct, or the transverse wave, 

 according to circumstances at the two stations, and hence, knowing 

 the time-interval between the marks on the plates, the velocity of 

 propagation could readily be calculated. 



As the result of these observations the surprisingly low velocity of 

 438 feet per second for the direct, and 357 feet per second for the 

 transverse wave, was obtained. The soft nature of the material 

 through which the disturbance was propagated is given as the 

 probable reason for this result. 



The results of similar experiments by Mr. Robert Mallet, at the 

 Hellgate explosions, in New York Harbour, are referred to. At the 

 conclusion of the paper an example of the records obtained in actual 

 earthquakes is given and briefly described. 



VIII. On the Electrolytic Diffusion of Liquids." By G. Gore, 

 LL.D., F.R.S. Received November 8, 1881. 



In a paper on the " Influence of Voltaic Currents on the Diffusion 

 of Liquids " (" Proc. Roy. Soc," vol. 32, 1881), I described a number 



