ON THE VOLCANIC PHENOMENA OF JAPAN, 



223 



tremors were observed out of the total number of observations made at 

 any particular gradient are also given. 



The general conclusion to be drawn from this table is that tremors are 

 proportionately more frequent the steeper the gradient. 



(e) The -presence of tremors and the absence of loind. — In the detailed 

 wind analysis table c it was shown that there were tremors 10 times when 

 it was calm, and 53 times when there was only a light breeze in Tokio. 

 It was, however, also shown that although the wind was light the baro- 

 metric gradient ia relatively high. This led me to inquire whether there 

 was not a strong wind blowing at a distance from Tokio, while in Tokio 

 itself when tremors were observed it was calm. The results of the 

 inquiry were as follows : — 



First, in 6 cases out of the 10 when tremors were recorded during a 

 calm, there were heavy winds blowing behind the mountains which shelter 

 Tokio on its western and northern sides at a distance of 60 to 100 miles. 

 In 3 cases there was a calm throughout Central Japan, but the tremors 

 on these occasions were very slight. 



Second, on 35 days out of 45 days on which the 53 cases of tremors 

 were recorded with a Hght breeze, there was a strong wind blowing 

 within 50 to 150 miles of Tokio. When the wind was blowing up from 

 the S.W. at right angles to the ranges sheltering the plain of Tokio the 

 tremors were very marked. On 10 days there was a calm in Central 

 Japan, and the tremors which were recorded cannot be explained as the 

 result of wind, neither do they hold any connection with a steep baro- 

 metric gradient. 



It is proper to note here that 44 days when there was a calm in 

 Tokio, and no tremors, were also examined, with the result of show- 

 ing that on 22 of the days there was a general calm in Central 

 Japan, and on the 22 remaining days there was practically a calm. 

 At one or two stations only was the intensity of the wind one or 

 two, and even then at different stations it was blowing in contrary 

 directions. 



( f) Absence of tremors and presence of ivind. — By reference to section c, 

 it will be seen that there were sixteen cases when the wind was of strength 

 3, and one when the wind was of strength 4, and no tremors were 

 recorded. In these instances if tremors are the result of wind, then 

 tremors ought to have been recorded. In three cases the wind was local, 

 while in the remaining cases the wind came in from the ocean. 



(g) Analysis of selected storms. — A few of the more important tremor 

 storms, some of which extended over thirty or forty hours, have been 



