THE GREAT EARTHQUAKE OF S. E. JAPAN 143 



earth-movemeiity and the possible effects on land and sea in the 

 disturbed area, whicli now I find to have been not so much mistaken. 



Perhaps our readers niay feel convinced of the conclusiveness of 

 such evidence even when we are furnished with seismographic obser- 

 vations from a single station only and nothing else ; yet it may 

 interest some of you if I explain a method of determining the seismic 

 focus. As you know, earthquake movements consist of waves of two 

 different kinds when the origin is near us; namely, first, the elastic 

 or longitudinal waves, and second, the rigid or transverse waves. 

 The former are quicker in transit speed, but smaller in vibration 

 range than the latter, which constitute the principal portion of the 

 earth-movements. The transit speed of the initial phase of the elastic 

 waves is as high as about 5.5 km. per sec, while that of the rigid 

 waves is about 3.2 km. per sec. The instrumental observation of the 

 initial earthquake movement gives the direction of the origin, and the 

 difference of time arrivals of the two different waves, which is com- 

 monly called the duration of the preliminary tremors, gives the dis- 

 tance between the focus and tlie observatory. Thus you will see that 

 these two data aid us in determining the position of the origin. 



Soon after the first shock, fire broke out at two j^laces in the 

 university, and within one and a half hours, our Institute was envel- 

 oped in raging smoke and heat ; the shingles, now exposed to the 

 open air, as the tiles had fallen down as a result of the shock, began 

 to smoke and eventually took fire three times. I can not tell you 

 how desperately I fought against the fire without water or any hel]! 

 from outside, commanding at the same time the rest of the men to 

 carry away the more imjiortant things into safe places. It was 10 

 o'clock at night before I found our Institute and Observatory quite 

 safe. Whenever I recollect the scene of that calamitous day and 

 evening, I camiot help feeling deeply grateful to our men for having 

 ])erformed their duty so well ; for, even an assistant, who had been 

 lying in tlie University Hospital, and a mechanician, who had been 

 on holiday in tlie city, came to the Institute at once, and we all, 10 

 in number, did our best jmi'tly in continuing earthquake observations, 

 and partly in extinguishing the fire, taking no food or drink till mid- 

 night, while four of us who were residing in the lower i)art of the 

 town lost our houses and pro})erty by fire. (PI. XXIV A.) 



3. Seismographs. Most of the seismographs in the Institute 



