ntinuous_, was very great, and might be taken for
some of the harder and denser rock formations at 11,000 or 12,000 feet
per second. That these enormous velocities of wave transit would be
something near those of actual earthquake shock seemed probable to me,
and was so accepted by Hopkins.

Thus, he says (Report, p. 88): "The velocity of the sea-wave, for any
probable depth of the sea, will be so small as compared with that of the
vibratory wave, that we may consider the time of the arrival of the
latter at the place of observation as coincident with that of the
departure of the sea-wave from the centre of divergence."

In my original Paper (Dynamic, &c.), I had suggested, as an important
object, to ascertain by actual experiment what might be the wave's
transit rate in various rocky and incoherent formations; and having
proposed this in my first "Report upon the Facts of Earthquake" to the
British Association, I was enabled by its liberality to commence those
experiments, in which I was ably assisted by my eldest son, then quite a
lad--Dr. Jno. William Mallet, now Professor of Chemistry at the
University of Virginia, U.S.; and to give account of the results, in my
second Report ("Report, British Association for 1851") to that body.

Those experiments were made by producing an impulse at one end of an
accurately measured base line, by the explosion of gunpowder in the
formation experimented upon, and noting the time the elastic wave
generated required to pass over that distance, upon a nearly level
surface. Special instruments were devised and employed, by which the
powder was fired and the time registered, by touching a lever which
completed certain galvanic contacts. The media or formations in which
these experiments were conducted were, damp sand--as likely to give the
minimum rate--and crystalline rock (granite), as likely to give the
maximum. The results were received, not with doubt, but with much
surprise, for it at once appeared that the actual velocity of transit
was vastly below what theory had indicated as derivable from the density
and modulus of elasticity of the material, taken as homogeneous, etc.
The actual velocities in feet per second found were:

In sand 824.915 feet per second.
In discontinuous and
much shattered granite 1,306.425 " "
In more solid granite 1,664.574 " "

This I at once attributed, and as it has since been prove