Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/413

348 of the widening and flattening of the annular wave upon the surface of still water, as it is transmitted outwards from the point at the centre, whence the impulse emanated. And in such case, the extinction of the wave must depend, upon its velocity falling to the point at which, the molecular constitution of elastic solids is such, as to cease to transmit its movements, further, from particle to particle. Which of those views, or whether either, expresses what actually occurs in nature, I believe physicists have as yet not determined. Nor are the variables, of velocities and amplitudes, which I have been able to obtain in the present case, capable of more than affording a general indication on the subject. The velocities, indeed, have been fixed with a good deal of precision and certainty; but I have been unable to obtain, any better means of approximation to the amplitude, at diflferent points, than those afforded by the width, at the level of the centre of gravity, of fissures, formed through and remaining in, great masses of very inelastic masonry. The obtaining more precise results as to amplitude, remains for the reward of future seismic observers.

On comparing the few cases in which, for the same locality, I was able to obtain, both velocity and amplitude, (the latter approximately,) and choosing such stations only, as are situated nearly in one right line, passing through the seismic vertical—i.e., having a nearly common wave-path, and therefore less exposed to local disturbing causes, (which change both velocity and amplitude often suddenly and without regard to distance from the origin)—comparing such, it will be found, that we have very probable indications, of increase of amplitude, as the distance from the seismic