Among the most interesting features of the planet's surface are the round, or oval spots which Lowell calls oases; these invariably occur at the junction of the canals. "In spite of the great number of the spots, not one of them stands isolate. There is not a single instance of a spot that is not connected by a canal to the rest of the dark areas." There appears to be no spot that has not two or more canals running to it, and apparently no canal junction is without its spot. The majority of the spots are 120 to 150 miles in diameter. There are many smaller ones. These spots, like the canals, appear and disappear coincidently with seasonal changes. The canals and the oases follow the same method and order in their growth. "Both are affected by one progressive change that sweeps over the face of the planet from the pole to the equator." The reader cannot dwell too strongly on the fact that the visibility of these various markings appears first in northern latitudes, and gradually darkens toward the equator, precisely the reverse of the unfolding of plant life on the Earth. From Mars our Earth would show its tropical vegetation the year round, while in Mars no tropical vegetable coloration would appear until water from the melting polar snow caps animates its growth. Lowell shows conclusively that the seas are not seas, nor the canals waterways, nor the spots lakes. Apparently, the spots appear not so much by an increase in size as by a deepening in tint. They start, it would seem, as big as they are to be, but faint in tone; they then proceed to darken throughout. If these spots are areas of vegetation, the explanation of their appearance is at once evident. Even more markedly unnatural is another phenomenon of this phenomenal system, of which almost every one has heard and almost nobody has seen,--the double canals. Upon a part of the disk where, up to that time, a single canal has been visible, of a sudden, some night, in place of the single canal, twin canals are perceived, similar in character and inclination, absolutely parallel, reminding one of the twin rails of a railroad track. The regularity of the thing is startling. In details the doubles vary, chiefly, it would seem, in the distance the twin lines lie apart. Lowell says the widest he has seen is the Ganges, in which six degrees separate the two lines,--in the narrowest, the Phison, four degrees and a quarter. From 120 to 175 miles of clear country is found between the paralleling lines. "One element of mystery may be eliminated at the outset.... It is perceived of a sudden, by the observer, because of some specially favorable night. But it has been for some time developing. So much is apparent from my observations. Suggestions of duality occurred weeks before the thing stood definitely revealed. Furthermore, the gemination may lie concealed from the observer some time after it is quite complete, owing to lack of favorable atmospheric conditions. For it takes emphatically steady air