222 



REPORT 1887. 



With a wind velocity of 700-750 kilometres per 24 hours, tremors 

 were observed in 100 per cent, of the times of observation. 



With a wind velocity of 750-800 kilometres per 24 honrs, tremors 

 were observed in 100 per cent, of the times of observation. 



(c) Detailed wind analysis.— The analysis now referred to extends 

 over the period between Jan. 20 and May 14, 1886, or nearly four 

 months. The wind observations with which the tremors were compared 

 are given in the tri-daily weather maps prepared by the Imperial 

 Meteorological Observatory. The wind scale runs from 0, or a calm, to 

 6, or a hurricane. 



With the wind at tremors were observed 10 times and not observed 

 16 times. 



With the wind at 1 tremors were observed 53 times and not observed 

 47 times. 



With the wind at 2 tremors were observed 54 times and not observed 

 49 times. 



With the wind at 3 tremors were observed 37 times and not observed 

 16 times. 



With the wind at 4 tremoi's were observed 12 times and not observed 

 1 time. 



The percentage of times that tremors were observed with the wind in 

 different states were as follows : — 



Wind at 0, percentage 38 

 )) )) Ij >i 53 



5) )) 2, „ 53 



„ „ 3, „ 70 



„ „ 4, „ 92 



From this and the preceding analysis it seems that the stronger the 

 wind the more likely it is that tremors should occur. The difficulty 

 which here presents itself is to account for tremors sometimes occurring 

 during a calm, and for the occasional absence of tremors during a wind. 

 A partial explanation of these difficulties is obtained when we compare 

 the occurrence of tremors with the barometric gradient, when we find 

 that for each particular state of the wind when tremors have occurred 

 the gradient has been steeper than the gradient for the same state of the 

 wind when tremors have not occurred. Thus — 



From the above it appears that tremors are more closely connected with 

 barometric gradient than they are with a local wind. 



((Z) Detailed barometric analysis. — The following table shows the 

 relationship between the occurrence of tremors and the barometric gra- 

 dient, irrespective of the force of the wind. The percentage of times that 



