208 EEPORT— 1882. 



tbe Hakodate homoseist this shock travelled at the rate of about 

 10,219 feet per second to reach Tokio. Between Tokio and Yokohama 

 the rate of propagation appears to have been about 4,500 feet per second. 



2. The earthquake of February 6, and two disturbances on March 1,1881. 

 These disturbances, like that of October 25, appear to have travelled 



in a straight line through Tokio and Yokohama. Their velocities of propa- 

 gation were respectively about 3,900, 1,900, and 1,400 feet per second. 



3. The earthquake of February 16, 1881. 



This shock appears to have originated in Yedo Bay, about eight miles 

 east of Yokohama. From the Yokohama homoseist the velocity with 

 which the shock travelled on to Tokio was about 2,454 feet per second. 



4. The earthquake of March 11, 1881. 



This disturbance originated at a place about nineteen miles S.S.W. 

 from Chiba. The shock was a severe one. From the Tokio homoseist 

 it appears to have travelled at the rate of 2,200 feet per second on to 

 Yokohama. 



No doubt, notwithstanding the care which has been taken to have 

 the time observations correctly recorded, it is possible that there may be 

 errors due, for instance, to observers or instruments at the different 

 stations making their records at different portions of the disturbance. 

 Also there may be differences in the calculated velocities due to differences 

 in the topographical and geological nature of the districts traversed by 

 the disturbance. 



Although causes such as these may lead to a want of accuracy in the 

 calculations which are here presented, I still regard the results of these 

 calculations as indicating general laws. This view appears to be confirmed 

 by the analysis of a table of earthquake velocities which I have compiled from 

 the writings of various earthquake investigators, and also from the result of 

 experiments on artificially produced disturbances yet to be referred to. 



III. The Kature of EarthqtiaJie Motion. 



In my first report to this Association I stated, 1st, that although the 

 upper portions of buildings may at the time of an earthquake move 

 through a considerable distance, the actual motion of the ground does not 

 usually exceed a few millimetres, and is often under one millimetre ; 

 2nd, the backward and forward motions of the ground are very irregular, 

 both as regards period and amplitude ; 3rd, that there are seldom more 

 than two or three vibrations per second ; and 4th, that the motion often 

 takes place in more than one direction. 



To these observations, which have received further confirmation from 

 records of earthquakes taken during the past year, I may add that in 

 certain earthquakes where there are one or more prominent vibrations or 

 what might be called shocks — 



1st. That the motion of the ground imvards towards the origin of the 

 disturbance is usually much greater than the motion outwards. 



2nd. That the velocity, and consequently the acceleration of an earth 

 particle for the inward motion, is usually very much greater than for 

 the outward motion. 



In certain instances these two characters — which are of great import- 

 ance, not only as indicators of the side from which the disturbance came, 

 but also as indicators of the nature of the cause of the disturbance — I 

 have sometimes observed, not simply in one or two vibrations of a dis- 

 turbance, but in nearly all the vibrations which were sufficiently well 

 defined to be analysed. 



