EFFECTS PEODUCED UPON BUILDINGS. 109 



subjected to a series of shocks, similar to those which they 

 experienced before being cracked, still continued to give 

 way, the extremities of a considerable number of cracks in 

 the N.E. end of the museum buildings of the Engineering 

 College were marked with pencil. Although since the 

 time of marking there had been many severe shocks, these 

 cracks did not visibly extend. These marks were made 

 on the outside wall of the building. On the inside, one of 

 these same cracks showed itself as a fissure about ^ inch 

 in width. Across this crack a horizontal steel wire 

 pointer was placed. One end of this wire was fixed in 

 the wall; the other end, which was pointed, rested on 

 the surface of a smoked glass plate placed on the other 

 side of the crack. After small earthquakes there was no 

 indication of motion having taken place, but after a shock 

 on February 21, as indicated by a line upon the smoked 

 glass plate, it was seen that the sides of the crack had 

 approached and receded from each other through a distance 

 of about -J^ inch. 



By similar contrivances placed on cracks in a neigh- 

 bouring building exactly similar results were obtained, 

 namely, that during small earthquakes the two sides of 

 the crack had retained their relative positions, but at the 

 time of a large shock this position had been changed. 



In this building it was also observed that the cracks 

 in many instances increased their length. 



By attaching levers to the end of the pointers to 

 multiply any motion that might take place, no doubt the 

 indications would be more frequent and more definite. It 

 would also be easier to note the relative distances of motion 

 in two directions, namely, how far the cracks had closed 

 and how far they had opened. As to whether motion 

 would occur or not, much would no doubt depend upon 

 the direction of the earthquake. 



