250 



SEKIYA AND OMORT. 



March 20th, 1885, with those obtained on the surface ground about 

 30 feet distant he found that they were in the ratios of 1 : 34, 

 1:52 and 1 : 82 respectively. But for small disturbances, tlie records 

 in the pit did not differ much from those on the surface. The 

 observations we have made are really a continuation of Prof. Milne's, 

 the same method being adopted in both cases. The results con- 

 tained in the present paper also show in certain cases some difference 

 of movement on the free surface and in the pit. 



The observations were made in the Imperial University at Hongo, 

 Tokyo, where the soil is hardened alluvium. The pit is 4 feet square 

 and 18 feet deep, and is situated only a few yards distant from the 

 instruments in the Seismological Observatory. Its bottom is ]iaved with 

 bricks to a thickness of about 2 feet. The soil appears here to be very 

 homogeneous, so that there will be little difference in earth-shakings 

 arising from the heterogeneity of ground between the surftice and the 

 bottom of the pit. 



Comparison of the Instruments used on the Surface 

 and in the Pit. 



The comparison in tlie present paper is restricted to the horizontal 

 components of earth movements. The instruments employed were Prof. 

 'I. A. Ewing's Horizontal Pendulum Seismographs. For earthquakes 

 which are not too great these instruments give diagrams which 

 represent practically absolute motions of the ground.* 



The instruments used in the pit and on the surface were made 

 as much alike as possible. To compare their action, they were 

 placed on a shaky table, and their diagrams for the same motion were 



• See Memoirs of the Science Dep., Univ., Tokyo : No. 9, and the Jour. Science Coll., Imp. 

 University, Vol. I. 



