Telescopically examined, Mars is always found to exhibit patches of shade of various sizes and shapes, and, on the whole, fairly permanent from year to year. During the last few years in particular these markings have been subjected to very careful scrutiny and measurement at the hands of numerous observers of skill and experience, and armed in many cases with very powerful telescopes. The conjoint effect of the observations obtained has been largely to augment our knowledge of the planet’s geography, or (to use the proper term) “areography.” Before describing the minutest details recorded and pencilled by the best observers, it will be best to speak of the leading general features which are within the grasp of comparatively small telescopes—say, refractors of 6 inches and reflectors of 12 inches in aperture. The first thing which presents itself as very obvious on the disc of Mars, is the fact that certain portions are ruddy, whilst others are greenish in hue. It is generally assumed that the red areas represent land and the green areas water. On this subject Sir John Herschel’s remarks, penned about half a century ago, may be said still to stand good. He ascribes the ruddy colour to “an ochrey tinge in the general soil, like what the red sandstone districts on the Earth may possibly offer to the inhabitants of Mars, only more decided.” The propriety of this thought will be best appreciated by a reader who has travelled through parts of North Gloucestershire, and seen a succession of ploughed fields in that locality. The deep red colour of the soil is in many places very conspicuous. It has often been remarked that the redness of Mars is much more noticeable with the naked eye than with a telescope; and Arago carried this idea one step further in suggesting that the higher the optical power the less the colour. This, however, might naturally be expected.