EFFECTS PEODUCED UPON BUILDINGS. 



117 



independent of each other, would be different. On 

 account of this difference in period, whilst one portion of 

 a building is endeavouring to move towards the right, 

 another is pulling towards the left, and, in consequence, 

 either the bonds which join them or else they themselves 

 are strained or broken. This was strikingly illustrated 

 by many of the chimneys in the houses at Yokohama, 

 which by the earthquake of February 20, 1880, were 

 shorn off just above the roof. The chimneys were shafts of 

 brick, and probably had a slower period of vibration than 

 the roof through which they passed, this latter vibrating 

 with the main portion of the house, which was framed of 

 wood. 



A particularly instructive example of this kind which 

 came under my notice is roughly sketched in fig. 25, 



This is a chimney standing alone, which, for the sake 

 of support, was strapped by an iron band to an adjoining 

 building. It would seem that at 

 the time of the shock, the building 

 moving one way and the chimney 

 another, the swing of the heavy 

 building gave the chimney a sharp 

 jerk and cut it off. The upper 

 portion, being then loose upon the 

 lower part, rotated under the in- 

 fluence of the oscillations in manner 

 similar to that in which grave- 

 stones are rotated. 



Mallet made observations similar to these in Italy. 

 He tells us that a buttress may often not have time to 

 transmit its stability to a wall. The wall and the 

 buttress have different periods of vibration, and therefore 

 they exert impulsive actions on each other. Effects like 

 these were strikingly observable in many of the rural 



Fig. 25. 



