In many ways Mars resembles our earth; it has atmosphere, seasons, storms, clouds and mountains. Vast white patches which have the appearance of snow and ice cover both its poles; these are found to vary in size with the seasons, being largest during the Martian win ter, and sometimes even completely disappearing during the summer. The "Canalli,° or chan nels, which have become known through the in exact English translation of Canals, were first mapped in large numbers by the Italian astron omer, Schiaparelli, although a few of them had been previously observed by other astron omers. They consist of narrow, dark lines, generally straight, forming a network over the whole surface of the planet. Some of the observers, however, deny the extreme regular ity of these curious features, describing them as of varying widths and of a somewhat irregular appearance. At their junctions we often find small dark areas known as oases. Large dark ish gray and green areas of the planet have been named seas, but it is now certain from the amount of permanent detail which is de tected in them that they are not bodies of water. In fact, the course of many of the canals can be traced across these greenish areas. It is, indeed, certain that Mars approxi mates to a desert planet and that there is but little water on its surface. The greater area of the planet is of a yellowish or orange color and these regions are believed to be true deserts.
It is thought by some of the students of the planet that the greenish areas are vegetation, that the canals are strips of irrigated country and that the polar caps are true deposits of snow or ice, the melting water of which is artifi cially led to dryer regions of the planet. To this explanation many astronomers vigorously dis sent, their objections being principally based on the extremely light atmosphere of the planet, its probable very low temperature, and espe cially upon the uncertainties still remaining in our ideas of the appearance of the Martian surface and in the interpretation of what has been seen. It is to be hoped that at the very favorable oppositions of 1924, 1939 and 1941 a more definite basis may be acquired for ex tending our knowledge in this fascinating field. The reader will find tolerably complete state ment of the known and supposed facts and of the various inferences drawn from them among the titles given below. Consult Flam marion, Camille, 'La Planete Mars et ses con ditions d'habitilite> (1892) ; Lowell, Percival, 'Mars and its Canals' (1906), and 'Mars as the Abode of Life' (1909) ; Wallace, Alfred Russell, 'Is Mars Inhabited?' (1907).
Eitic Director of Flower Astronomical Observatory, University of Pennsylvania.