READER, the evidence I am about to present will satisfy you, not
only that a comet might have struck the earth in the remote
past, but, that the marvel is that the earth escapes collision
for a single century, I had almost said for a single year. How
many comets do you suppose there are within the limits of the
solar system (and remember that the solar system occupies but an
insignificant portion of universal space)? Half a dozen-fifty-a
hundred-you will answer. Let us put the astronomers on the
witness-stand: Kepler affirmed that "COMETS ARE SCATTERED
THROUGH THE HEAVENS WITH AS MUCH PROFUSION AS FISHES IN THE
OCEAN." Think of that! "Three or four telescopic comets are now
entered upon astronomical records every year. Lalande had a list
of seven hundred comets that had been observed in his time."
Arago estimated that the comets belonging to the solar system,
within the orbit of Neptune, numbered seventeen million five
hundred thousand! Lambert regards five hundred millions as a
very moderate estimate! [1. Gu