These little moons are certainly among the most curious and interesting bodies of the solar system; but, unfortunately, the sight of them is denied to most observers. That they were not seen by Sir William Herschel with his great 4-foot reflector probably only points to the superior defining power of the 26-inch Washington refractor as compared with Herschel's celebrated but cumbrous instrument. Still, they were missed by many telescopes quite competent to show them, and of as good defining quality as the Washington instrument--a fact which goes to add proof, if proof were needed, that the power which makes discoveries is the product of telescope × observer, and that of the two factors concerned the latter is the more important. It is said that the moons have been seen by Dr. Wentworth Erck with a 7-1/3-inch refractor. The ordinary observer is not likely to catch even a glimpse of them with anything much smaller than a 12-inch instrument, and even then must use precautions to exclude the glare of the planet, and may count himself lucky if he succeed in the observation. A word or two may be said as to what a beginner may expect to see with a small instrument. It has been stated that nothing under 6 inches can make much of Mars; but this is a somewhat exaggerated statement of the case. It is quite certain that the bulk of the more prominent markings can be seen with telescopes of much smaller aperture. Some detail has been seen with only 1-3/4-inch, while Grover has, with a 2-inch, executed drawings which show how much can be done with but little telescopic power. The fact is, that observers who are only in the habit of using large telescopes are apt to be unduly sceptical of the powers of small ones, which are often wonderfully efficient. The fine detail of the canal system is, of course, altogether beyond small instruments; and, generally speaking, it will take at least a 4-inch to show even the more strongly marked of these strange features. At the 1894 opposition, the writer, using a 3-7/8-inch Dollond of good quality, was able to detect several of the more prominent canals, but only on occasions of the best definition. The accompanying rough sketch (Fig. 24) gives an idea of what may be expected to be seen, under favourable conditions, with an instrument of between 2 and 3 inches. It represents Mars as seen with a glass of 2-5/8-inch aperture and fair quality. The main marking in the centre of the disc is that formerly known as the Kaiser or Hour-glass Sea. Its name in Schiaparelli's nomenclature, now universally used, is the Syrtis Major. The same marking will also be seen in Mr. Phillips's drawing of 1899, January 30, in which it is separated by a curious bright bridge from the Nilosyrtis to the North. The observer need scarcely expect to see much more than is depicted in Fig. 24, with an instrument of the class mentioned, but Plate XX. will give a very good idea of the