EFFECTS PRODUCED UPON BUILDINGS. 115 



From this it would seem that such a house must have 

 rocked from side to side one foot out of its normal 

 perpendicular position. That the motion was great is 

 testified by nearly all who tried to stand at the time of 

 the shock, it having been impossible to walk steadily 

 across the floor of a room in an upper story. The houses 

 here referred to are either those which are purely 

 Japanese, or else those which are framed of wood and 

 built on European models, a class of building which is 

 very common in Tokio and Yokohama. 



Perry and Ayrton calculated the period of a complete 

 natural vibration of different structures. For a square 

 house whose outer and inner sections were respectively 

 30 and 26 feet, and whose height was 30 feet, the period 

 calculated would be about '06 second. 



At the time of the above earthquake many houses 

 seem to have moved like inverted pendulums. On the 

 morning after the shock my neighbour, who was living 

 upstairs in a tall w^ooden house with a tile roof, told me 

 that he endeavoured to count the vibrations, and was of 

 the impression that to make a complete swing it took 

 about 2 seconds. 



Assuming now that the distance through which the 

 top of a wooden house moved was about 1 foot, and the 

 number of vibrations which it made per second was 

 about '5, then the greatest velocity of a point on the top 

 of such a house must have been about 6 feet per second. 



Mallet, who made observations upon the vibrations of 

 various structures, tells us that Salisbury spire moves to 

 and fro in a gale more than 3 inches. A well-constructed 

 brick and mortar wall, 40 feet high and 1 foot 6 inches 

 thick, was observed to vibrate in a gale 2 feet trans- 

 versely before it fell. 



An octagonal chimney with a heavy granite capping, 



