EARTH TREMORS. 



325 



air. The extent of these sudden variations was approxi-. 

 mately from '03 to '05 inches. Eeckoning an increase 

 of barometrical pressure of one hundredth of an inch as 

 equivalent to a load of twenty million pounds on the square 

 mile, during this storm there must have been the equiva- 

 lent of loads of from 60 to 100 million pounds to the square 

 mile continually placed on and removed from a considerable 

 tract of the earth's surface. If the period of application 

 of these stresses approximately coincide with the natural 

 vibrational period of the area affected, it would surely 

 seem, especially when we reflect upon the effect of an 

 ordinary carriage, that tremors of considerable magnitude 

 ought to be produced. 



An inspection of the following few observations taken 

 from my note-book for the same typhoon will suggest that 

 even the large and slower variations are capable of pro- 

 ducing tremulous motions. 



Time 













Barometer 



h. m. reading 



12 5 P.M 2902 



12 10 „ 













2905 



12 12 „ 











« 



29-07 



12 13 „ 













29-05 



12 25 „ 













29-10 



12 50 „ 













29-00 



1 10 „ 













29-00 



120 „ 





, 









. 29-07 



