appearance of the planet when viewed with a telescope of considerable power. The polar caps will be within reach, and sometimes present the effect of projecting above the general level of the planet's surface, owing, no doubt, to irradiation. [Illustration: FIG. 24. MARS, June 25, 1890, 10 hours 15 minutes; 2-5/8-inch, power 120.] To the intending observer one important caution may be suggested. In observing and sketching the surface of Mars, do so _independently_. The chart which accompanies this chapter is given for the purpose of identifying markings which have been already seen, not for that of enabling the observer to see details which are beyond the power of his glass. No planet has been the cause of more illusion than Mars, and drawings of him are extant which resemble nothing so much as the photograph of an umbrella which has been turned inside out by a gust of wind. In such cases it may reasonably be concluded that there is something wrong, and that, unconsciously, 'the vision and the faculty divine' have been exercised at the expense of the more prosaic, but in this case more useful, quality of accuracy. By prolonged study of a modern chart of Mars, and a little gentle stretching of the imagination, the most unskilled observer with the smallest instrument will detect a multitude of canals upon the planet, to which there is but one objection, that they do not exist. There is enough genuine interest about Mars, even when viewed with a small glass, without the importation of anything spurious. In observation it will be noticed that as the rotation period of Mars nearly coincides with that of the earth, the change in the aspect presented from night to night will be comparatively small, the same object coming to the meridian thirty-seven minutes later each successive evening. Generally speaking, Mars is an easier object to define than either Venus or Jupiter, though perhaps scarcely bearing high powers so well as Saturn. There is no planet more certain to repay study and to maintain interest. He and Jupiter may be said to be at present the 'live' planets of the solar system in an astronomical sense. [Footnote *: The opposition of a planet occurs 'whenever the sun, the earth, and the planet, as represented in their projected orbits, are in a straight line, with the earth in the middle.'] [Footnote †: That point in the orbit of a planet or comet which is nearest to the sun.] CHAPTER IX THE ASTEROIDS