ON THE EARTHQUAKE A>D VOLCANIC PHEXOMENA OF JAPAN. 



ISl 



was usually near to this point that 

 fracturing ocouri'ed. 



4. Experiments on the Vibration 

 of Chirntieys and BuHd'uujs. — Short- 

 ly after my fire Professors Tanaka- 

 Jate, Mano, and other Members of 

 the Earthquake Committee to which 

 I am attached took diagrams of the 

 natural vibrations of the brick chim- 

 ney stack which was left standing 

 after my fire. The chimney is 18 

 feet in height, and has a rectangular 

 section of 3 feet 8 inches by 3 feet 

 1 inch and two flues. With a rope 

 and a windlass, a deflection of the 

 top of the stack of one inch and a 

 half was obtained, when the rope 

 was suddenly released The result 

 was that the chimney vibrated for 

 about 20 seconds, and a record of 

 these vibrations was obtained upon 

 a band of paper. One of the dia- 

 grams is reproduced, tig. 19. The 

 period of motion has apparently 

 varied with thfe range of swing ; for 

 example — 



Kange of Motion 1-25 in Period 17 second. 

 i> >i I) ''^o „ ,, '85 ,, 

 M „ „ -10,, „ -43 „ 



When we i-emember that the greatest 

 portion of the destruction occasioned 

 by earthquakes is due to the fact 

 that various portions of a building, 

 in consequence of not synchronising 

 in their movements, are mutually 

 destructive, while solitary structures 

 may be destroyed in consequence 

 of the agreement between their 

 natural period and that of an earth- 

 quake, it seems likely that observa- 

 tions like the one now described may 

 lead to important rules being for- 

 mulated for builders. 



The next experiments will be on 

 the vibration of wooden buildings. 



5. The Earth Waves of Earth- 

 quakes. — On several occasions the ap- 

 paratus described in the Report for 

 1893 has given diagrams showing the 

 amount of tilting which accompanies 

 certain earthquakes. The period of 

 these angular displacements closely 

 coincides with the periodicity of hori- 



