120 EARTHQUAKES. 



hama earthquake of February 1880 by the knocking over 

 of chimneys. The particular case of the chimneys is, 

 however, better illustrated by the next experiment. 



Fourth Experiment — Take a little block of wood 

 three-quarters of an inch square and about one inch high, 

 and place it on the top of A, b, or c. It will be found 

 that, although the spring on which it stands is caused to 

 swing backwards and forwards through a distance of three 

 inches, the little block will retain its position. 



This little block we may regard as the upper part of a 

 chimney standing on a vibrating stack, and we see that, 

 so long as this upper portion is light, it has no tendency 

 to fall. 



Fifth Exjperiraent. — Eepeat the fourth experiment, 

 having first placed a small leaden cap on the top of the 

 block representing the chimney. (The cap used only 

 weighed a few grammes.) When vibration commences 

 it will be found that the block quickly falls. This would 

 seem to indicate that chimneys with heavy tops are more 

 likely to fall than light ones. 



Sixth Experiment. — Bind A and B together with a 

 strip of paper and stand the little block upon the top of 

 either. It will be found that the block will stand as in 

 the fourth experiment. 



Seventh Experi-nient. — Bind A and c, or B and c 

 together, and place the block upon the top of either of 

 them. When vibration commences, although the paper 

 may not be broken, the little block will quickly fall. 



Eighth Experiment. — Take two pencils or pieces of 

 glass tube and place them under the board D E. If the 

 table F G be now shaken in the direction D E, it will be 

 found that the springs will not vibrate. 



In a similar manner if a house or portion of a house 

 were carried on balls or rollers, as has already been sug- 



