ON TUE EARTHQUAKE AND VOLCANIC PHENOMENA OF JAPAN. 305 



best, it must not be overlooked that there have been exceptional cases 

 where buildings in such localities have suffered, as, for example, in Yoko- 

 hama in 1880, and to a certain extent in Calabria in 1783. 



In Tokio, as the result of our feelings, it has been shown that earth- 

 quakes are more often felt on the high ground than upon the low 

 ground. Instrumental observations so far as they have gone, and the 

 results of experience in 1855, have, however, shown that the most de- 

 structive motions have been experienced on the low ground. (See 'Distri- 

 bution of Earthquake Motion in a small Area,' by J. Milne, ' Trans. Seis. 

 Soc.,' vol. xiii.) 



The best sites in a city may be determined, should it be thought ad- 

 visable, by means of a specially organised seismic survey, which involves 

 placing a number of similar seismographs throughout a city, and a proper 

 comparison of the records they furnish. By doing this it has been shown 

 that a seismic survey may be made for a small piece of ground, say one 

 quarter square mile or less in area. Such a sui'vey was made of the 

 compound of the late Imperial College of Engineering, now the Gaku- 

 shuin, in Tokio. The results obtained clearly showed that if we had two 

 similar houses on that compound at a distance of less than 800 feet apart, 

 by a given earthquake one of these houses might be destroyed, and the 

 other suffer little, if any, damage. Until this survey was made it was 

 not suspected that the difference in motion of two sides of that particular 

 piece of ground could be so pronounced. Very wet ground or ground 

 that is marshy notably forms a bad foundation. Steep-sloping ground is 

 also bad, the alluvial materials resting on such a surface often sliding 

 downwards, much in the same manner as tiles may slide from a steeply- 

 pitched roof. The sliding, or tendency to slide, is in all probability aggra- 

 vated when the surface is loaded by a building. 



The upper edges of cliffs and scarps, where the motion of the free face 

 of the cliff or scarp is naturally large, are also dangerous situations, and 

 these more especially when the strata dip outwards. 



2. Foundations. 



As a result of observations made in a pit about 10 feet in depth, it 

 was found that the motion at the bottom of the pit was in strong earth- 

 quakes very much smaller than it was upon the surface. These observa- 

 tions led to the conclusion that great advantages might be gained by 

 giving a building a deep foundation, this advantage being increased if the 

 building rose freely, as in a house with an open area and a basement. 

 That at least there is no harm in such a structure is attested by the fact 

 that in all earthquake countries where there is legislation respecting 

 building, cellars or basement stories are recognised as admissible. That 

 relatively but little motion enters a building with such foundations is also 

 attested by the fact that for such cellars vaulting is allowed, whereas for 

 stories above the ground floor it has invariably been suppressed. My own 

 experiments in this direction gave a measurement of the relative motion 

 above and below ground ; showing that deep foundations were not simply 

 without danger, but they might be advantageous. As, however, the ex- 

 periments have only been made at one point, and as they are of so much 

 importance to builders, it is desirable that they should be repeated. 



The Ischian regulations provide that buildings should be founded on 

 the most solid ground. If, however, the ground was soft, a platform of 



1889. X 



V 



