1898-99.] Prof. Knott on Earthquake Vibrations. 
581 
the boundary, the smaller the amount of energy which passes 
through into the second medium, and the greater the amount of 
energy thrown hack into the first. 
In a seismological paper published * some ten years ago, I dis- 
cussed at length the reflection and refraction of waves at a surface of 
rock and water. Some of the main results arrived at in regard to the 
reflection and refraction of elastic waves at the boundary of rock and 
water are indicated in the following diagrams (fig. 3). Each figure 
Fig. 3. 
shows approximately the manner in which the energy of a particular 
type of wavejat a particular angle of incidence is distributed among 
its derivatives of both types. The incident ray is represented by the 
broadest line passing downwards from left to right. The upper 
medium is rock, and the lower water. Since condensational waves 
* Republished, with extensions and additions, in the Philosophical 
Magazine for July 1899. 
