of some millions of years, to destroy all traces
of a place of intersection of their orbits, if it once existed. But if
this be admitted why need the hypothesis be abandoned? Given such
duration of the Solar System as is currently assumed, there seems no
reason why lapse of a few millions of years should present any
difficulty. The explosion may as well have taken place ten million years
ago as at any more recent period. And whoever grants this must grant
that the probability of the hypothesis has to be estimated from other
data.

As a preliminary to closer consideration, let us ask what may be
inferred from the rate of discovery of the planetoids, and from the
sizes of those most recently discovered. In 1878, Prof. Newcomb, arguing
that "the preponderance of evidence is on the side of the number and
magnitude being limited", says that "the newly discovered ones" "do not
seem, on the average, to be materially smaller than those which were
discovered ten years ago"; and further that "the new ones will probably
be found to grow decidedly rare before another hundred are discovered".
Now, inspection of the tables contained in the just-published fourth
edition of Chambers' _Descriptive Astronomy_ (vol. I) shows that whereas
the planetoids discovered in 1868 (the year Prof. Newcomb singles out
for comparison) have an average magnitude of 11.56 those discovered last
year (1888) have an average magnitude of 12.43. Further, it is
observable that though more than ninety have been discovered since Prof.
Newcomb wrote, they have by no means become rare: the year 1888 having
added ten to the list, and having therefore maintained the average rate
of the preceding ten years. If, then, the indications Prof. Newcomb
names, had they arisen, would have implied a limitation of the number,
these opposite indications imply that the number is unlimited. The
reasonable conclusion appears to be that these minor planets are to be
counted not by hundreds but by thousands; that more powerful telescopes
will go on revealing still smaller ones; and that additions to the list
will cease only when the smallness ends in invisibility.

Commencing now to scrutinize the two hypotheses respecting the genesis
of these multitudinous bodies, I may first remark concerning that of
Laplace, that he might possibly not have propounded it had he known that
instead of four such bodies there are hundreds, if not thousands. The
supposition that they resulted from th