immaterial phantoms, unreal visions of that negative shadow-kind
which has been alluded to. This, however, unfortunately, is not a
permissible alternative in the circumstances of the case. The great
underlying and indispensable fact that the comet comes rushing up
toward the sun out of space, and then shoots round that great center
of attraction by the force of its own acquired and ever-increasing
impetuosity; the fact that it is obedient

{p. 78}

through this course to the law of elliptical, or, to speak more
exactly, of conic-section, movement, _permits of no doubt as to the
condition of materiality_. The comet is obviously drawn by the
influence of the sun's mass, and is subservient to that all-pervading
law of sympathetic gravitation that is the sustaining bond of the
material universe. _It is ponderable substance beyond all question_,
and held by that chain of physical connection which it was the glory
of Newton to discover. If the comet were not a material and
ponderable substance it would not gravitate round the sun, and it
would not move with increasing velocity as it neared the mighty mass
until it had gathered the energy for its own escape in the enhanced
and quickened momentum. In the first instance, the ready obedience to
the attraction, and then the overshooting of the spot from which it
is exerted, combine to establish the comet's right to stand ranked at
least among the ponderable bodies of space."[1]

And it is to the comet we must look for the source of a great part of
those vast deposits of gravel which go to constitute the Drift.

"They have been usually attributed to the action of waves; but the