74 Mr. Mauuet on the Dynamics of Earthquakes. 
the line of transit of the earth wave, the effect of the arrival of the earth wave 
at the watery fissure will be, at the instant, to compress its walls more or less 
together, and so squeeze out the water, which will, for a moment, gush up at the 
spring head, like a fountain, and again remain in repose after the transit of the 
wave. The inertia of the fluid will aid this effect at the instant of transit of 
the rearward slope of the wave over the spring, that is to say, at the moment 
that the ridge of the wave sinks again, on passing over the spring, the water 
will appear to rise.* To this many other such curious, mimute, accidental earth- 
quake consequences might be added and explained, but it would be a tedious 
and useless labour, as the explanations of all such will be apparent easily to 
those acquainted with physics, where the conditions have been properly ob- 
served. 
Before leaving the subject of the great earth wave, however, it is necessary to 
make some observations as to the change which will take place (under certain 
circumstances of geological formation) in the transit of the wave, by which, in 
place of its progressive motion, the whole country will move, or be more or 
less completely shaken at the same instant of time, so as, in fact, to produce 
one simultaneous shock over a larger or smaller space at the same instant. 
Where a wave of elastic compression, suck as our earth wave, passes 
through a body, varying, in specific elasticity, in several parts of its course, or 
passes from one body to another of different elasticity, at each such change of 
medium the wave changes its velocity, and in part changes its course, a portion 
being reflected and a portion refracted, analogous to a wave of light, in passing 
through media of variable density or of different refractive indices; so also, if 
the wave passes from a highly elastic body to one of very low elasticity, and again 
into a third body of high elasticity, in proportion as the wave continues un- 
broken, the bodies must have a common time of vibration or of wave transit, at 
the surfaces of contact. A popular illustration of these truths is afforded by a 
glass of sparkling champagne, which will not ring clear when the glass is struck, 
while the foam continues to crown the liquor, but no sooner has its disappear- 
ance enabled the glass and the wine to vibrate, as a system, than the tone becomes 
musical. 
* Fluids and all loose bodies may also be thrown upwards, when the direction of wave transit 
is vertical or nearly so, 
