When approaching inferior conjunction—­i.e., passing between the earth and sun—­Venus appears, with a telescope, in the shape of a very thin crescent.  Professor Lyman watched this crescent, becoming narrower day after day as it approached the sun, and noticed that its extremities gradually extended themselves beyond the limits of a semicircle, bending to meet one another on the opposite side of the invisible disk of the planet, until, at length, they did meet, and he beheld a complete ring of silvery light, all that remained visible of the planet Venus!  The ring was, of course, the illuminated atmosphere of the planet refracting the sunlight on all sides around the opaque globe.

In 1874 M. Flammarion witnessed the same phenomenon in similar circumstances.  One may well envy those who have had the good fortune to behold this spectacle—­to actually see, as it were, the air that the inhabitants of another world are breathing and making resonant with all the multitudinous sounds and voices that accompany intelligent life.  But perhaps some readers will prefer to think that even though an atmosphere is there, there is no one to breathe it.

[Illustration:  VENUS’S ATMOSPHERE SEEN AS A RING OF LIGHT.]

As the visibility of Venus’s atmosphere is unparalleled elsewhere in the solar system, it may be worth while to give a graphic illustration of it.  In the accompanying figure the planet is represented at three successive points in its advance toward inferior conjunction.  As it approaches conjunction it slowly draws nearer the earth, and its apparent diameter consequently increases.  At A a large part of the luminous crescent is composed of the planet’s surface reflecting the sunshine; at B the ratio of the reflecting surface to the illuminated atmosphere has diminished, and the latter has extended, like the curved arms of a pair of calipers, far around the unilluminated side of the disk; at C the atmosphere is illuminated all around by the sunlight coming through it from behind, while the surface of the planet has passed entirely out of the light—­that is to say, Venus has become an invisible globe embraced by a circle of refracted sunshine.

We return to the question of life.  With almost twice as much solar heat and light as we have, and with a deeper and denser atmosphere than ours, it is evident, without seeking other causes of variation, that the conditions of life upon Venus are notably different from those with which we are acquainted.  At first sight it would seem that a dense atmosphere, together with a more copious supply of heat, might render the surface temperature of Venus unsuitable for organic life as we understand it.  But so much depends upon the precise composition of the atmosphere and upon the relative quantities of its constituents, that it will not do to pronounce a positive judgment in such a case, because we lack information on too many essential points.