The way in which these thirty-nine articles fit into one another to a mortised whole is striking enough at first sight, but becomes more and more impressive the more one considers it. For some are due to one kind of observation, some to another. In the taking they are unrelated; yet in the result they agree. Equally pregnant is the history of their acquisition. Most of them were detected as the outcome of observations at the opposition of 1894, and led to the theory which was published in the writer’s first book on the subject. Others are the result of the five oppositions that have since occurred. These have proved entirely corroborative of the previous ones and of the theory then deduced, and that in two distinct ways: first, by the accumulated evidence they have brought to the matter along the old lines; and, secondly, by what they have revealed in new directions. Of these thirty-nine articles of Martian scientific faith in observation or deduction, (9), (10), (21), (22), (25), (27), (28), (30), (33), (35), (36), and (38) are in whole or part new. That continued scrutiny is thus corroborative of the earlier results, both along the old and along new lines of investigation, warrants additional confidence in the conclusion. Considering, now, these counts, we see that they make reasonably evident on Mars the presence of:— 1. Days and seasons substantially like our own; 2. An atmosphere containing water vapor, carbonic acid, and oxygen; 3. Water in great scarcity; 4. A temperature colder than ours, but above the Fahrenheit freezing-point, except in winter and in the extreme polar regions; 5. Vegetation. First and foremost of these is air. In order to make it possible for vital processes of any sort to take place, the body of a planet must be clothed with an atmosphere, by the modesty of nature, the old astronomers would have said. Such a covering subserves two purposes: it keeps out the cold of space, thus permitting the maintenance of a temperature sufficient to support life, and it affords a medium through which metabolism can go on. Now the presence of air is attested first and foremost by the fact of change in the Martian markings, (12), (13), (26), (28), and (35). The changes observed are conspicuous; are both inorganic (in the case of the polar caps), (12), (13), and (35), and metabolic or organic, (26) and (28), (in the case of the blue-green areas); that is, they consist of building up as well as of pulling down and are planet-wide in occurrence. Such changes could not occur in the absence of an atmosphere. They show that this atmosphere consists of water vapor, (5), carbonic acid, and oxygen, (28).