The most prominent surface marking on Mars is that known as the “Kaiser Sea,” sometimes called the “V-mark” from its resemblance to that letter, though a leg of mutton would be quite as good a simile. East of the Kaiser Sea and a little north of the planet’s equator is a well-defined dark streak known as “Herschel II. Strait”; whilst on the west side is another shaded area which has been called “Flammarion Sea.” These three features are so very conspicuous, that, provided the hemisphere in which they are situated is fairly in front of the observer, his telescope, if it will show anything on Mars, will show these. The white patches seen on certain occasions _at_ Mars’s N. pole and _close to_ its S. pole form another special feature of interest connected with this planet. It admits of no doubt whatever that these are immense masses of snow and ice which undergo at stated intervals changes analogous to the changes which we know happen in the great fields of ice situated in the regions of the Earth surrounding the Earth’s two poles. Not only do these white patches look like snow, but if attention is paid to the changes they undergo and the epochs at which the changes take place there will be found abundant confirmation of this theory, for these patches decrease in size when brought under the Sun’s influence on the approach of summer and increase again in size when the summer is over and winter draws near. In the second half of 1892 the Southern Pole was in full view, and during especially July and August the diminution of the snow area from week to week was very evident. Schiaparelli, who observed it with great attention during that season, noted at the commencement of the season that the snow reached at the first as far as latitude 70° and formed a polar cap some 1200 miles in diameter. Its subsequent decrease, however, was so marked that two or three months later the diameter of the snow patch had dwindled to no more than 180 miles, and became indeed still smaller at a later period. The summer solstice on Mars occurred on October 13, 1892, which was therefore the epoch of midsummer for Mars’s southern hemisphere. Whilst these changes were taking place in the southern hemisphere, no doubt changes of the reverse character were going on in the northern hemisphere, but they were not visible from the Earth because the North Pole was situated in that hemisphere of Mars which was turned away from the Earth. In previous years, however, the North Pole being turned towards the Earth its snow was also seen to undergo the same sort of change; in other words, was seen to melt. This happened, and was seen in 1882, 1884, and 1886. These observations of the alternate increase and decrease of the polar snow on Mars may be viewed with telescopes of moderate power, but of course it is more interesting and profitable to watch them with a large telescope. The fact (for it is an undoubted fact) that the north polar snow is