164 REPORT— 1895. 



automatically record the time at which a particular vibration was drawn. 

 At each of the observatories it is therefore possible to calculate the 

 instant at which a given instrument commenced to write its record. 



In 1891, on December 9 and 11, strong shocks originated in the 

 province of Noto on the west coast, which were observed in Gifu, Nagoya, 

 and Tokio. The mean velocity determined from these records was 

 2"31 km. per second. 



The destructive disturbance of October 28, 1891, which was recorded 

 in Europe, was followed by many after shocks, the times of arrival of 

 seventeen of which were accurately noted at Osaka, Nagoya, Gifu, and 

 Tokio. The origin of the main shock was about five miles to the west of 

 Gifu. To reach Tokio, a distance of 151 miles, took 120 seconds. The 

 average time taken for all eighteen shocks was 118 seconds, and the 

 average velocity was 2-40 Lm. per second, the rate of transmission to 

 Osaka being the same as it was over the much longer path to Tokio. 



The primary disturbance seems to have reached Shanghai at a rate of 

 about 1'61 km. per second, and Berlin at about 2-98 km. per second. 

 For the Shonai shock on October 22, 1894, as a mean obtained by the 

 method of least squares from observations at ten stations from 60 to 300 

 miles distant from the origin, a velocity of about 1*95 km. per second was 

 obtained. 



Giving these last determinations, all of which were computed by 

 Mr. F. Omori, weights proportional to the number of observations each 

 represents, the average rate at which disturbances are propagated over 

 long distances in Japan is 7,560 feet, or 2 3 km. per second, a rate which 

 fairly well agrees with that at which the large waves of similar dis- 

 turbances travel from Japan to Europe. 



?. Observations along Wave Paths of Great Leiigth. 



Next we will turn to earthquakes which have been noted at distances 

 from their origins greater than those at which it has been possible to 

 obser\e in Japan — a notable example of which are the observations made 

 at the time of the Charleston Earthquake on August 31, 1886. Over 

 400 ol)servations were made. A number of these were obtained from 

 clocks which had been stopped, and as many of these were regulators 

 which had daily been compared with a time signal, there is no reason to 

 doubt their accuracy. All these observations, which were made on wave 

 paths between 300 and 924 miles in length, were subjected to a rigorous 

 analysis by Professor Simon Newcomb and Captain Charles Dutton, with 

 the result that an average velocity of 5,184 m. was determined, and there 

 was no indication of any sensible variation in speed. Considering the 

 phase of motion which in the majority of instances was in all probability 

 observed, this result is remarkably high. 



A valuable study of the rate at which vibrations may be propagated 

 through the earth's crust is one made by Dr. G. Agamennone of a series 

 of shocks which in 1893 had their origin near to the island of Zante. 

 These were recorded at the various stations mentioned along the foot of 

 the diagram Fig. 15, the one farthest from the origin being Potsdam. The 

 lengths of the various wave paths are indicated in kilometres. The time 

 intervals naeasured vertically are on a scale of 20 seconds per millimetre. 

 For five shocks straight lines connect a series of points indicating the 

 differences in time between the occurrence of the shock near to its origin 



