One of the finest achievements of astronomy is having made man a citizen of the heavens. The planet which we inhabit is a heavenly body, just as is Venus, Mars, or Jupiter, and far from occupying the centre of creation, it lies in the depths of infinite space as do the most distant stars of the Milky Way. Venus possesses no more light of her own than does the Earth; she simply receives the rays of the Sun and sheds them into space as the Moon does. Take, for instance, a small finder telescope and direct it towards Venus; you will see the form of a crescent. It is no longer Venus, but Diana. Take a rather more powerful telescope, and you will see that the border of this crescent is not regular, and the southern pole is blunted and rounded, while the northern pole is pointed. On increasing the power of your instrument you will perceive the atmosphere by the gradual transition between the illuminated hemisphere and the dark hemisphere, or by the blinding clouds and light shadows which fleck its disc. If you go still farther and give yourself the pains and the pleasure of doing a few astronomical calculations, you will see that the diameter of its globe is just the same as that of the Earth--within one thousandth part!--but that Venus is a little lighter than the Earth, its density being only four-fifths of ours, whence it results that objects weigh a little less on its surface than they would on ours: 1,000 grammes transported on Venus would only weigh 880 grammes; on Mars they would weigh even less, viz. 376 grammes; and even less on the Moon, viz. 165 grammes. We are very heavy down here. Astronomy alone teaches us that this young sister of ours is in communication with us, not only by means of light, but also by attraction, and that space, so far from being a separation between worlds, is a real link, an invisible hyphen. For example, when the distance between us and Venus is 25 million miles, light only takes 2½ minutes to cross that distance. Is that a serious separation? Even in France a telegram, in spite of its name, takes more than an hour to be delivered a few hundred miles away, on account of intermediate links. If astronomers ever succeeded in establishing celestial telegraphy, communication would be much more rapid between one world and another than between one part of modern Babylon and another. An interplanetary telephone would be almost instantaneous. * * * * * If the luminous beams from Venus to the Earth only take two or three minutes to reach us, according to its proximity, the attraction between the two planets is transmitted still more rapidly, for it does not even take a whole second. And just think! At the distance of millions of miles we feel the mysterious influence of Venus, we abandon for a moment the regular course of our orbit round the Sun to follow in her path. Celestial mechanics calculates this displacement and accounts for it in its determinations.