108 EAETHQUAKES. 



The thickness of the walls in which these arches are 

 placed is 1 ft. 11 in. They are built of Japanese bricks 

 bound together with ordinary lime. The span of the 

 arches is 8 ft. 3 in., and the height of the arch from the 

 springing-line to the crown 4 ft. 1 in. The height of 

 the abutments is 7 ft. 1^ in. The voussoirs of the arch 

 are formed of a light grey soft volcanic rock, and on their 

 faces show a depth of 12 inches. The width, of the inter- 

 mediate columns between the arches is 4 ft. 6 J in. 



To determine whether at the time of an earthquake 

 there was any variation in the dimensions of these arches, 

 a light stiff deal rod, about 2 in. by ^ in. in cross section, 

 was placed across the springing-line of the arch. One end 

 of this was firmly fixed to the top of one abutment by 

 means of a spike ; on the other end, which was to indicate 

 any horizontal movement if the abutments approached 

 each other, there was fixed a pointer made out of a piece 

 of steel wire. This rested on a piece of smoked glass fixed 

 to the ledge on which the loose end of the rod was 

 resting. If the abutments approached or receded from 

 each other a line would bo drawn measuring the extent 

 of the motion. As a further indication of motion, a second 

 smoked glass plate was fixed on the transverse rod, which 

 plate was marked on by a pointer attached to a vertical 

 rod hanging down from the crown of the arch. 



As a general result of these experiments it may be 

 said that the portions of the building which were examined 

 usually either did not move at all, or else they practically 

 synchronised in their movements. When they did move, 

 the extent of motion was small, and the small differences 

 in movement which were observed were in every proba- 

 bility far within the elastic limits of the structure. 



Observations on Cracks. — To determine whether the 

 walls of a building which have once been cracked, when 



