nd we will never leave it as long as it lasts!" exclaimed the doctor.
"Just at this time it points like a long arrow out in the direction of
Mars. It is moving gradually as the Earth moves and hourly correcting
its aim. At opposition time it will point directly and unerringly at
Mars. Therefore it is a way prepared, surveyed, and marked for us
through the all-enveloping sunlight, which otherwise would be dreadful
enough."

"But how can we be sure of keeping in it? It is rapidly narrowing as it
reaches farther out."

"I see I should have explained that to you before I went to sleep, and
saved you this fright. The shadow now points behind Mars, as it is many
days yet before it overtakes that planet in opposition. That is why I
told you to steer always a little behind the planet. But you went a
little out of the course, and immediately something warned us. That rim
of light on the east of the Earth was notice to us that we were not in
the centre of the shadow, but bearing too far to the left. We must keep
absolutely in the dark of the Earth, with no light visible on either
side of it. If a thin rim should appear on one side, we must turn toward
the other until it is all dark again."

"Grant that this shadow is so enormously long, yet it is only scarcely
one-fortieth of the distance to Mars," I objected. "After we emerge from
it, what then?"

"With the aid of my telescope we shall probably be able to see the Earth
as an orb, half or quarter as large as the Moon usually appears to us,
and to observe its phases until we are several million miles from it. We
must continue to keep the rim of light, which will then surround it,
equal on all sides."

"Ah, but I am afraid," I interrupted, "that as soon as we pass out of
this shadow the sunlight will be so bright that we cannot see any
planets, not even the Earth. You know we cannot see the Moon only a
quarter of a million miles away when the sun shines."

"In that case we must move the telescope to your window, put on a
darkened lens, and steer so as to keep the Earth as a spot in the middle
of the Sun. It must appear to us as Venus does to the Earth when she is
making a transit across the face of the sun. But by our continual
shifting we prevent the Earth from making a transit, and hold it as a
steady spot in the centre of the Sun. This we can do for many, many
million miles, continuing until we have reached the vicinity of Mars.

"And you must also remember," continued t