126 



EEPORT — 1892. 



part of the plain the direction of motion, similarly determined, must have 

 been more north and south. 



From the measurements of maximum acceleration, and from the 

 records of seismographs which at Nagoya and Gifu gave for the com- 

 mencement of the disturbance the period of the back and forth motions, 

 we may approximately- determine the amplitude and maximum range of 

 motion. The following are a few of such determinations, which it will 

 be observed do not materially differ from the width of fissures found in 

 the open country. The period taken is one and a half second : — 



It must be remembered that all the numbers given referring to 

 acceleration and range of motion only apply to the open plain, and not 

 to free surfaces like river banks or lines of soft material like river-beds. 

 A phenomenon which seemed to accompany most, if not all, of the 

 Nagoya-Gifu shocks was a hollow, booming sound. These sounds, which 

 accompany all great earthquakes, and even small ones, if they occur in 

 rocky regions, have been discussed at considerable length in the ' Transac- 

 tions of the Seismological Society' (see vol. xii. p. 53, and p. 115). They 

 are evidently the result of vibrations conveyed through the earth, and 

 may be continuous with the large vibrations which constitute the earth- 

 quake. Professor Tanakadate endeavoured to determine the intervals in 

 time between the sounds and the subsequent shakings. Sometimes there 

 was an interval of one or two seconds, whilst at other times the two 

 phenomena were synchronous. The distance of the point of observation 

 from the origin of these disturbances was in all probability at least 10 or 

 12 miles. While the writer was at Nagoya, which may have been 

 from 25 to 35 miles distant from the earthquake origins, the 

 sounds never preceded a shaking by more than two seconds. Some- 

 times they were synchronous, and often there were sounds without any 

 subsequent shaking. 



Very many observations were made in Tokio, on the Gifu Plain, and 

 in other places, to determine the velocity of propagation. These have not 

 yet been computed, but disturbances appear to have reached Tokio at 

 rates of about 8,000 feet per second. 



From observations made at the Zikawei Observatory, near Shanghai, 

 which is, roughly, 1,000 miles distant, the velocity with which the move- 

 ment was transmitted was about 5,104 feet per second. As stated in 

 newspapers, the time taken to reach the Berlin Astronomical Observatory, 

 in round numbers, was forty-nine minutes, the velocity of transmission 

 being about 9,840 feet per second. The disturbance appears also to have 

 been noted at the Magnetical Observatory in Potsdam. 



Although numerous experiments and observations have been made to 

 determine the velocity with which motion is conveyed through the earth, 

 we have not as yet any satisfactory explanation of the great diflFerences 

 which have been observed. 



From a long series of experiments, extending over several years, 

 which were made in Tokio, where earth disturbances were caused by 



