ON THE EARTHQUAKE AND VOLCANIC rHENOMEXA OF JAPAN. 103 



disturbance, and with different systems of observation, I determined 

 velocities lying Ijetween 630 (192 m.) and about 200 (61 m.) feet per 

 second. 



4. In my experiments the vertical free surface wave had tJie quickest 

 rate of transit, the normal being next, and the transverse motion being 

 the slowest. 



T). The rate at which the normal motion outraces the transverse 

 motion is not constant. 



6. As the amplitude and period of the normal motion approach in 

 value to those of the transverse motion, so do the velocities of transit of 

 these motions approach each other. 



(6) Observations on Earthquakes. 



The observations quoted in this section commence with those where 

 the wave paths have not been more than a few hundred feet from station 

 to station. These arc followed by the results obtained from instruments 

 separated from each other by distances of from three to six miles, a few 

 hundred miles and so on up to velocities determined over paths equal to 

 a quarter of the earth's circumference. 



1. Observations in Japan. 



For several years the author took diagrams of earthquakes at seven 

 stations, each about 900 feet apart. These stations were in electrical 

 connection, so that one pendulum marked time intervals upon each of the 

 moving sui'faces upon which diagrams were being drawn. From tifty sets 

 of diagrams, representing fifty different earthquakes, it was only in five 

 instances that the same wave could be identified at the different stations. 

 The result of these identifications led to calculation of velocities of 1,787, 

 1,302. 1,825, 869, and 501 metres per second. 



Even these determinations cannot be accepted without reserve, 

 because it is found that waves may spread out as they pass from station 

 to station, a given wave splitting up into two waves, &c. Hence a 

 velocity calculated from a ivave (a) may be different from a velocity of a 

 leave (b), and yet both are -part of the same disturbance. In the diagram 

 from one station a large wave may have a slight notch upon its crest, at 

 another station this notch is seen to have increased in size, while at a 

 third station it is so large that the single wave appears as two waves. 

 As in the artificially produced disturbances, although an earthquake 

 becomes feebler as it radiates, it apparently increases in its duration. 



The same system of observation has recently been elaborated in 

 Japan, but the distances between stations have been increased to several 

 miles. Because the commencement of a disturbance at a given station 

 varies with the sensibility given to the seismograph, the determinations 

 of velocity depend upon the identification of particular waves upon the 

 diagrams obtained from at least three stations. Up to the present this 

 has only been possible on one or two occasions. On November 30, 1894, 

 at 8.30 p.m., a velocity of 5 km. per second was obtained, other dis- 

 turbances giving from 2'4 to 3"6 km. per second. 



The following are examples of velocity determinations made in Japan 

 between stations which have access to the telegraphic system of the 

 country, and which are provided with seismographs and clocks which 



M 2 ' 



