the transit of December 5, 1882. As the dark planet impinged on the
bright sun, it of course cut out a round notch from the edge of the
sun. At first, when this notch was small, nothing could be seen of the
outline of that part of the planet which was outside the sun. But when
half the planet was on the sun, the outline of the part still off the
sun was marked by a slender arc of light. A curious fact was that this
arc did not at first span the whole outline of the planet, but only
showed at one or two points. In a few moments another part of the
outline appeared, and then another, until, at last, the arc of light
extended around the complete outline. All this seems to show that while
the planet has an atmosphere, it is not transparent like ours, but is
so filled with mist and clouds that the sun is seen through it only as
if shining in a fog.

Not many years ago the planet Mars, which is the next one outside of
us, was supposed to have a surface like that of our earth. Some parts
were of a dark greenish gray hue; these were supposed to be seas and
oceans. Other parts had a bright, warm tint; these were supposed to be
the continents. During the last twenty years much has been learned as
to how this planet looks, and the details of its surface have been
mapped by several observers, using the best telescopes under the most
favorable conditions of air and climate. And yet it must be confessed
that the result of this labor is not altogether satisfactory. It seems
certain that the so-called seas are really land and not water. When it
comes to comparing Mars with the earth, we cannot be certain of more
than a single point of resemblance. This is that during the Martian
winter a white cap, as of snow, is formed over the pole, which
partially melts away during the summer. The conclusion that there are
oceans whose evaporation forms clouds which give rise to this snow
seems plausible. But the telescope shows no clouds, and nothing to make
it certain that there is an atmosphere to sustain them. There is no
certainty that the white deposit is what we call snow; perhaps it is
not formed of water at all. The most careful studies of the surface of
this planet, under the best conditions, are those made at the Lowell
Observatory at Flagstaff, Arizona. Especially wonderful is the system
of so-called canals, first seen by Schiaparelli, but mapped in great
detail at Flagstaff. But the nature and meaning of these mysterious
lines are sti