Chronicle was careful to notice) from Poynings;
and Mr. Curruthers felt much conscious self-
approval for having written it, and especially
for having timed the writing of it so well.
"Sooner, he might have made an excuse of it
for coming here," thought the astute gentleman;
"and it would have been heartless not
to have written at all."

For once in his life, Mr. Carruthers of Poynings
had written a letter of importance.

GAPS IN THE SOLAR SYSTEM.

GAPS in the Solar System is the title of a
very interesting little paper which M. Radau
has lately contributed to the Revue des Deux
Mondes, anent Le Verrier's startling announcement,
that there ought to be some planet or
planets between the sun and Mercury. Most of
us have heard of "Bode's Law." The name,
by the way, is doubly wrong, for it was a small
German astronomer, named Titius, who
discovered the curious analagoy which the great Bode,
of Berlin, talked so much about, and thought
so much of, that at last his name got coupled
with it; and it is not a law at all, but a trick of
numbers, like that which was published lately in
the newspapers about Louis Napoleon's life.
Take the series, 0, 3, 6, 12, 24, 48, 96, 192 (each
term of which, except the first, is double of the
term before it); add 4 to each, and you have 4,
7, 10, 16, 28, 52, 100, 196, of which, all except
the 28 and the 196, were found to answer pretty
well for the distances of the planets known in
Bode's time. "Herschel," "Uranus," or
"Georgium Sidus," as he is "indifferently"
styled, brought the law into immense favour.
"Uranus," it is true, was discovered accidentally;
but as soon as his orbit was determined,
it was seen that 196 would stand tolerably
enough for his distance from the sun as
compared with that of the other planets; and so
Bode's law got into such credit that everybody
was wild about number 28. Zach
calculated beforehand the elements of the planet
which he felt must be there, evolving (German
fashion) the facts out of his interior consciousness.
Lalande divided the heavens among four-
and-twenty astronomers, and had a long and fruitless
search made for the missing star. And so
Bode's law, again, did no good; for, after all,
Piazzi, of Palermo, who, in 1801, found out
"Ceres," as it is called, came upon it by accident,
and thought for some time it was a comet.
Indeed, it was very difficult to calculate the orbit of
such a shy little planet ; and when Gauss, then an
unknown young man at Göttingen, had done so,
and the Bodeites were beside themselves for
joy, Olbers threw everything wrong by finding
out another stranger, "Pallas," so close to
"Ceres" as apparently to destroy the "law" of
distances. This must be a comet, said everybody;
and some went so far as to assert that,
though tailless, it was surrounded by a hazy sort
of beard. But, pretty soon, "Juno" and
"Vesta," and ever so many more, appeared on
the scene. Retired doctors, Prussian
postmasters of country towns, everybody for a year
or two was always finding out a new planet;
and the only consolation was that their distances
all lay between 22 and 34, of which the
mean is 28. A more serious blow to the
so-called "law" of distances was the discovery
of "Neptune," just twenty years ago.
Some of us can remember how the scientific
world was divided, and how high party feeling
ran between the Adamites and the worshippers of
Le Verrier. The new planet could not be brought
under Bode's "law;" but its discovery was a
remarkable instance of the way in which observation
and theory supplement one other. Uranus
did not, somehow, go on as he ought. Though
not "discovered" till 1781, he had been
catalogued (generally as a new fixed star) from
time to time since 1690; but when Delambre
and Bouvard began to tabulate his motions,
they found that either the old observations
must have been singularly inexact, or that some
unknown force must be periodically acting upon
him. By-and-by Bouvard's tables became quite
useless, and he gave them to his nephew to be
corrected. Bessel, of Königsberg, writing to
Humboldt, talked of the trans-Uranian planet;
and so things went on, till in 1844 Adams drew
up a paper on the supposed orbit, which the
Greenwich authorities suffered to lie unused till
Le Verrier had announced (in June, 1846) that
he had approximately determined the planet's
position from the perturbations of Uranus. Then
Challis was set to work on Adams's paper, and
Galle, of Berlin, took Le Verrier's calculations.
Challis found the star on the 4th of August, but
marked it at first as a fixed star, not recognising
its true character till the very end of September.
Galle found it on the 23rd of September, the very
day on which Le Verrier's papers reached him.
Bode's law, then, has been going out of favour;
no one would think, now-a-days, of quoting it to
prove that a planet cannot exist in such and
such a position. The perturbation method, on the
other hand, so successful in discovering planets,
has received additional confirmation from
the fact that certain unexplained periodical
oscillations of Sirius have been found to
depend on a satellite, long suspected, but only
discovered four years ago by the American
astronomer, Mr. Alvan Clark. Well, then, says Le
Verrier, how do you account for the irregular
movements of Mercury? They differ from the
perturbations of Venus or any of the rest,
and cannot (as far as we know) be explained
except by supposing that somewhere in the
"intra-Mercurial space" there is a mass of
matter, possibly minutely divided, sufficient to
find this second group of asteroids, if such a
group there is, is a difficult matter. Mercury
himself is not the most easily observed of the
planets; and, with the sun so near, such small
bodies may well escape the best telescopes and
the most eager eyes. The attempt has often
been made to fix on certain "spots in the sun"
as planetary bodies; the misfortune is, they