634 SCIENCE PROGRESS 



higher clouds, great changes and even reversals in the direction 

 of the wind may take place in the lower or upper regions of the 

 atmosphere. Such conditions favour the production of a silent 

 zone. On the whole, taking all the various conditions into 

 account, Mr. Fujiwhara has shown that a silent zone should be 

 manifested quite as frequently as a continuous sound-area. 



Mr. Fujiwhara has also considered the relations which exist 

 between the state of the weather and the forms of the sound- 

 areas in Japan. Under normal winter conditions, he finds that 

 the sound-areas should be single, but that under abnormal 

 conditions, when cyclones exist to the north, east, and south of 

 the volcano, there might be a silent zone. In summer, on the 

 other hand, the usual conditions would favour the production 

 of a silent zone, and the exceptional conditions the occurrence 

 of a continuous sound-area. 



