un
expand in the sky to more than two and a half times its former
magnitude, while the solar heat poured upon them swiftly augments from
something more than four and a half times to above eleven times the
amount received upon the earth! Then, immediately, the retreat of the
planet begins, the sun visibly shrinks, as a receding balloon becomes
smaller in the eyes of its watchers, the heat falls off as rapidly as it
had previously increased, until, the aphelion point being reached, the
process is again reversed. And thus it goes on unceasingly, the sun
growing and diminishing in the sky, and the heat increasing and
decreasing by enormous amounts with astonishing rapidity. It is
difficult to imagine any way in which atmospheric influences could
equalize the effects of such violent changes, or any adjustments in the
physical organization of living beings that could make such changes
endurable.

But we have only just begun the story of Mercury's peculiarities. We
come next to an even more remarkable contrast between that planet and
our own. During the Paris Exposition of 1889 a little company of
astronomers was assembled at the Juvisy observatory of M. Flammarion,
near the French capital, listening to one of the most surprising
disclosures of a secret of nature that any _savant_ ever confided to a
few trustworthy friends while awaiting a suitable time to make it
public. It was a secret as full of significance as that which Galileo
concealed for a time in his celebrated anagram, which, when at length he
furnished the key, still remained a riddle, for then it read: "The
Mother of the Loves imitates the Shapes of Cynthia," meaning that the
planet Venus, when viewed with a telescope, shows phases like those of
the moon. The secret imparted in confidence to the knot of astronomers
at Juvisy came from a countryman of Galileo's, Signor G. V.
Schiaparelli, the Director of the Observatory of Milan, and its purport
was that the planet Mercury always keeps the same face directed toward
the sun. Schiaparelli had satisfied himself, by a careful series of
observations, of the truth of his strange announcement, but before
giving it to the world he determined to make doubly sure. Early in 1890
he withdrew the pledge of secrecy from his friends and published his
discovery.

No one can wonder that the statement was generally received with
incredulity, for it was in direct contradiction to the conclusions of
other astronomers, who had long