ON THE VOLCANIC PHENOMENA OF JAPAN. 221 



As confirmatory of the above conclusion the preceding table for days 

 when there has either been great or little microseismical disturbance has 

 been drawn up. It shows the intensity of the tremors in Italy, the actual 

 height of the barometer, and the gradient. 



From an inspection of the table it will be seen that a low barometer, 

 as on March 29, is not necessai-ily accompanied with unusual tremors, 

 and that tremors only occur with a steep gradient. 



A steep gradient is usually accompanied by wind, but, unfortunately, 

 the means of comparing microseismical disturbances with the state of the 

 wind is not given on the Italian maps. 



Worlc done in Japan. — I will now give the general results derived 

 from a set of records obtained from my automatic tremor- recorder. With 

 but few omissions they extend from Jan. 13, 1885, to May 14, 1886. 



(a) General harometric analysis. — With the barometer standing above 

 the monthly mean tremors were observed 72 times, while they were not 

 observed 14-3 times. 



With the barometer below the monthly mean tremors were observed 

 105 times, while in 104 cases they were not observed. The observations 

 apparently indicate that tremors occur rather with a low than with a 

 high barometer ; but even if the barometer is low it is as likely that 

 tremors should not occur as it is that they should occur. The tables 

 showing these results also showed that tremors were more frequent 

 during the winter months — a fact which has often been noticed. 



(?;) General ivind analysis. — Tables were prepared, showing for each 

 month the number of times that tremors had been observed, or had not 

 been observed, for different intensities of the wind. The general results 

 arrived at showed that when the wind velocity was low it was seldom 

 that tremors had been observed, but when it was high tremors were 

 almost invariably observed. 



With a wind velocity of 100-150 kilometres per 24 hours, tremors 

 were observed in 28 per cent, of the times of observation. 



With a wind velocity of 150-200 kilometres per 24 hours, tremors 

 were observed in 27 per cent, of the times of observation. 



With a wind velocity of 200-250 kilometres per 24 hours, tremors 

 were observed in 24 per cent, of the times of observation. 



With a wind velocity of 250-300 kilometres per 24 hours, tremors 

 were observed in 34 per cent, of the times of observation. 



With a wind velocity of 300-350 kilometres per 24 hours, tremors 

 were observed in 50 per cent, of the times of observation. 



With a wind velocity of 350-400 kilometres per 24 hours, tremors 

 were observed in 35 per cent, of the times of obsei'vation. 



With a wind velocity of 400-450 kilometres per 24 hours, tremors 

 were observed in 54 per cent, of the times of observation. 



With a wind velocity of 450-500 kilometres per 24 hours, tremors 

 were observed in 57 per cent, of the times of observation. 



With a wind velocity of 500-550 kilometres per 24 hours, tremors 

 were observed in 38 per cent, of the times of observation. 



With a wind velocity of 550-600 kilometres per 24 hours, tremors 

 were observed in 60 per cent, of the times of observation. 



With a wind velocity of 600-650 kilometres per 24 hours, tremors 

 were observed in 44 per cent, of the times of observation. 



With a wind velocity of 650-700 kilometres per 24 hours, tremors 

 were observed in 62 per cent, of the times of observation. 



