The planet Mercury is, like the earth and the moon, a globe of dark matter which only shines and is visible by the illumination of the solar light. Its motion round the central star, which brings it sometimes between the sun and us, sometimes in an oblique direction, sometimes at right angles, and shows us a part incessantly variable, of its illuminated hemisphere, produces in its aspect, as seen in a telescope, a succession of phases similar to those which the moon presents to us. The cut represent the apparent variations of size and the succession of phases, visible in the evening after sunset; when the planet attains its most slender crescent, it is in the region of its orbit nearest to the earth, and passes between the sun and us; then, some weeks afterwards, it emerges from the solar rays and passes again through the same series of phases in inverse order, as we see them by reversing the figure. [Illustration: PHASES OF MERCURY BEFORE INFERIOR CONJUNCTION--EVENING STAR.] Venus, the second inferior planet, is nearly the same size as our earth. Seen from the earth, she is one of the most brilliant and beautiful of all the planets. Her speed is three miles a second faster than ours, and her distance from the sun is about two-thirds that of our own; so that the orbit of Venus lies half-way between the orbit of Mercury and the orbit of the earth. The day of Venus is about half an hour shorter than ours. Her year is nearly two hundred and twenty-five days, or seven and a half of our months. One or two astronomers have fancied that they caught glimpses of a moon near Venus; but this is still quite doubtful, and indeed it is believed to have been a mistake. Venus and Mercury are only visible as morning and evening planets. Venus, being farther from the sun, does not go before and follow after him quite so closely as Mercury, and she is therefore the longer within sight. When Venus, traveling on her orbit, comes just between the sun and us, her dark side is turned towards the earth, and we can catch no glimpse of her. When she reaches that part of her orbit which is farthest from us, quite on the other side of the sun, her great distance from us makes her light seem less. But about half-way round on either side, she shows exceeding brilliancy, and that is the best view we can get of her. Seen through a telescope, Venus undergoes phases like those of Mercury, or of our moon. That is to say, we really have “new Venus,” “quarter Venus,” “half Venus,” “full Venus,” and so on.