256 SEKIYA AND OMORI. 



from the actual diagrams, are arranged in tabular form. Notwith- 

 standing tlie frequent occurrence of earthquakes in Tokyo, simul- 

 taneous records of the pit and the surface instruments have been 

 obtained for a comparatively small number of earthquakes. This was 

 owing to the difficulty of managing the underground instrument. 



(1.) — January 15th, 1887. — This was an earthquake of unusual 

 severity a full account of which has already l^een given.* The beginning 

 portions of the surface and pit diagrams are given in PI. XXXVI. j^j" 

 and these for the convenience of comparison are placed side ]\y side. 

 Fig. 3 is for the E.AY. component, and Fig. 4 is for the N.S. component. 

 The glass plate whicli received the record of the surface instrument 

 made one revolution in 128 sec, and that of the pit instrument in 68 

 sec, so that the latter moved nearly twice as quick as the former. 

 Such 11 difference of the rate of revolution w<juld however cause no 

 material difference in the diagram. In these, as well as in the follow- 

 ing diagrams, the corresponding parts are marked with the same 

 alphabets, and the short radial lines mark the successive seconds 

 counted from the beginnings of shocks. 



The earthquake begins as usual with tremors. After a few 

 seconds, the motion liecomes suddenly great. The character of 

 the motion is striking. The ripples are very prominerit, and these 

 are superimp<^sed on slower undulations, whose period is alxjut 2 sec. 

 in the E.W. component, and about 3 sec in the N.8. component. 

 After a short time the ripples become less evident but the amplitude 

 of the motion continues to be great, and the maximum displacement 

 occurs at a point marked o in tlie E.W. component. Comparing now 

 the surface and pit diagrams, we see that the latter is much smoother 



* See the Journal of the College of Science, Imperial University, Japan, Vol. I., Part Til. 

 or Transactions of the Seismological Society of Jajoan, Vol. XI. 



t The complet ' diagram of the surface instrument is given in the same volumf s as cited 

 a bove. 



