136 EARTHQUAKES. 



Yokohama suffered more than those situated in the settle- 

 ment. This explanation is given on account of the great 

 authority it claims as a consequence of its source. It is 

 not clear how the statement can be supported, as different 

 portions of the mountain receive momentum in opposite 

 directions at the same time. 



Want of support on the faces of hills. — When a 

 wave of elastic compression is propagated through a 

 medium, we see that the energy of motion is being con- 

 tinually transmitted from particle to particle of that 

 medium. A particle, in moving forwards, meets with an 

 elastic resistance of the particles towards which it moves, 

 but, overcoming these resistances, it causes these latter 

 particles to move, and in turn to transmit the energy to 

 others further on. So long as the medium in which this 

 transfer of energy is continuous, each particle has a limit 

 to its extent of motion, dependent on the nature of the 

 medium. When, however, the medium, which we will 

 suppose to be the earth, is not continuous, but suddenly 

 terminates with a cliff or scarp, the particles adjacent to 

 this cliff or scarp, having no resistance offered to their 

 forward motion, are shot forward, and, consequently, the 

 ground here is subjected to more extensive vibrations 

 than at those places where it was continuous. This may 

 be illustrated by a row of marbles lying in a horizontal 

 groove ; a single marble rolled against one end of this 

 row will give a concussion which will run through the 

 chain, like the bumping of an engine against a row of 

 railway cars, and as a result, the marble at the opposite 

 end of the row, being without support, will fly off. 

 Tyndall illustrates the same thing Avith his well known 

 row of boys, each one standing with his arms stretched 

 out and his hands resting upon the shoulders of the boy 

 before him. A push being given to the boy at the back, 



