_VENUS, THE TWIN OF THE EARTH_ 46 A planet that matches ours in size--Its beauty in the sky--Remarkable circularity of its orbit--Probable absence of seasons and stable conditions of temperature and weather on Venus--Its dense and abundant atmosphere--Seeing the atmosphere of Venus from the earth--Is the real face of the planet hidden under an atmospheric veil ?--Conditions of habitability--All planetary life need not be of the terrestrial type--The limit fixed by destructive temperature--Importance of air and water in the problem--Reasons why Venus may be a more agreeable abode than the earth--Splendor of our globe as seen from Venus--What astronomers on Venus might learn about the earth--A serious question raised--Does Venus, like Mercury, rotate but once in the course of a revolution about the sun ?--Reasons for and against that view.