ox THE VOLCANIC PHENOMENA OF JAPAN. 



429 



completely unroofed, one of whicb -was a strong brick building. The 

 main timbers in certain roofs were broken. Grave-stones were rotated. 

 Many windows vrere broken, and bodies like the tops of stone lanterns, 

 corner stones of chimneys, &c., were projected. 



In Tokio a few chimneys fell, tiles were dislodged from the eaves of 

 buildings, and portions of a few walls were cracked or shattered. In some 

 instances these latter fell. 



In Yokohama the range of horizontal motion appears to have been 

 from 15 millimetres (f inch) to a maximum of 50 millimetres (3 inches). 

 Calculations of maximum velocity were made, but as the data on which 

 they were founded do not appear to have been satisfactory they are here 

 omitted. 



In Tokio the amplitude (range of motion) observed at Surugadai was 

 21 millimetres. Assuming the larger vibrations to have been performed 

 at the rate of one per second, this would indicate a maximum velocity of 

 60 millimetres per second, and a maximum acceleration of 360 millimetres 

 per second. With a period of two seconds, which is probably a more 

 correct assumption, the above quantities would respectively become 30 

 and 90 millimetres. 



October 15, 1884. — One or two chimneys fell in Tokio, plaster fell 

 from ceilings, and several brick walls were cracked. In Tokio, at Hitot- 

 subashi-soto the greatest horizontal motion observed was 43 milHmetres 

 and the period two seconds. This indicates a maximum velocity of 68 

 millimetres and a maximum acceleration of 210 millimetres. 



Januanj 15, 1887.' — This disturbance originated about 35 miles to 

 the south-west of Tokio. Near to its origin it destroyed many hura (fire- 

 proof storehouses built of wood, with a clay covering and a heavy roof of 

 tiles), and opened fissures in the ground. In Yokohama, say ten miles 

 from the origin, it destroyed many chimneys and slightly shattered 

 several buildings. In Tokio a few brick walls were slightly cracked. 



In Yokohama a horizontal motion of 35 millimetres was recorded. 



In Tokio the following observations were made : — 



Hitotsubashi 

 Hongo . 

 Chirikioku . 



Hongo and the Chirikioku (Imperial Meteorological Observatory) are 

 situated on moderately high ground, which is dry and hard. At Hitot- 

 subashi, which is low, the ground is damp and soft. 



The above measurements of range of motion and period were made on 

 solid foundations. The range of motion at the top of a building would 

 be greater while the period might be less. It seems from these observa- 

 tions that when there is an earth- movement of about 18 millimetres 

 (f inch) or over, it is likely that the period will be sufficiently short to 

 result in some form of destruction. 



Earthquakes of this description. Professor Sekiya observes, occur in 

 Japan about once a year, and near to Tokio every few years. 



' Trans. Seis. Soc. vol. ix. 



