Listen to Professor Young: "Its [Venus's] atmosphere is probably from one and a half to two times as extensive and as dense as our own, and the spectroscope shows evidence of the presence of water vapor in it." And Prof.William C.Pickering, basing his statement on the result of observations at the mountain observatory of Arequipa, says: "We may feel reasonably certain that at the planet's [Venus's] surface the density of its atmosphere is many times that of our own." We do not have to depend upon the spectroscope for evidence that Venus has a dense atmosphere, for we can, in a manner, _see_ her atmosphere, in consequence of its refractive action upon the sunlight that strikes into it near the edge of the planet's globe.

This illumination of Venus's atmosphere is witnessed both when she is nearly between the sun and the earth, and when, being exactly between them, she appears in silhouette against the solar disk.

During a transit of this kind, in 1882, many observers, and the present writer was one, saw a bright atmospheric bow edging a part of the circumference of Venus when the planet was moving upon the face of the sun--a most beautiful and impressive spectacle.
Even more curious is an observation made in 1866 by Prof.C.S.Lyman, of Yale College, who, when Venus was very near the sun, saw her atmosphere _in the form of a luminous ring_.

A little fuller explanation of this appearance may be of interest.
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.