The planets also come in for their share of examination. Mercury is so near the sun as seldom to be seen. Venus in small telescopes is only interesting with reference to her changes, like the moon, but in larger ones with great care the spots are visible. Mars is interesting as being so near a counterpart of our own planet. On it we see the polar snows, continents and seas, partially obscured by clouds, and these appearances are brought under our view in succession by the rotation of the planet. With a good six-inch glass and a power of 200 when the air is pure and the opposition is favourable, there is no difficulty in making out the coast-lines, and the various tones of shade on the water surface may be observed, showing that here the sea is tranquil, and there it is driven by storms. Up to very lately it was the only planet of considerable size further off the sun than Venus that was supposed to have no satellite; two of these bodies have however been lately discovered by Hall with the large Washington refractor of twenty-six inches diameter, and they appear to be the tiniest celestial bodies known, one of them in all probability not exceeding 10 miles in diameter. Jupiter and Saturn are very conspicuous objects, and the eclipses, transits, and occultations of the moons, and the belts of the former and rings of the latter, are among the most interesting phenomena revealed to us by our telescopes, while the delicate markings on the third satellite of Jupiter furnish us with one of the most difficult tests of definition. Uranus and Neptune are only just seen in small telescopes, and even in spite of the use of larger ones, we are in ignorance of much relating to these planets. The amateur will do well to attack all these with that charming book, the Rev. T. W. Webb’s _Celestial Objects for Common Telescopes_, in his hand. To observe the fainter satellites of the brighter planets, or, indeed, faint objects generally, near very bright ones, the bright object may be screened by a metallic bar, or red or blue glass placed in the common focus.