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Updated: June 28, 2025
They are seen to change in form and position from day to day, and Mr. Lowell is strongly of opinion that they are dust-storms, not what we term clouds. Suggested Explanation of the 'Oases. The numerous round dots seen upon the 'canals, and especially at points from which several canals radiate and where they intersect termed 'oases' by Mr. Lowell and 'craterlets' by Mr.
Those formed by cracks radiating from craterlets would also be subject to the same process of rounding off to an even greater extent; and thus would be produced the 'oases' of various sizes up to 50 miles or more in diameter recorded by Mr. Lowell and other observers. Probable Function of the Great Fissures. Mr.
The border is very irregular, and, according to Neison, consists on the E. of a precipitous cliff more than 9000 feet high. It is surrounded by a number of large rings on the S., and has several considerable small depressions on its N. border. There is apparently no prominent detail on the floor. Schmidt shows some ridges and craterlets.
Somewhat less than half of what we see of it consists of comparatively level dark tracts, some of them very many thousands of square miles in extent, the monotony of whose dusky superficies is often unrelieved for great distances by any prominent object; while the remainder, everywhere manifestly brighter, is not only more rugged and uneven, but is covered to a much greater extent with numbers of quasi-circular formations, differing widely in size, classed as walled-plains, ring-plains, craters, craterlets, crater-cones, &c.
It is well seen under a high light, as indeed is the case with most of these features. CRATERLETS, CRATER-PITS. To a great extent the former term is needless and misleading, as the so-called craters merge by imperceptible gradations into very minute objects, as small as half a mile in diameter, and most probably, if we could more accurately estimate their size, still less.
The region to the west is dotted over with innumerable minute craterlets. It has a central, many-peaked mountain about 2,400 feet in height. There is good reason to believe that the terracing shown in its interior is mainly due to the repeated alternate rise, partial congealation and retreat of a vast sea of lava. At full moon it is surrounded by radiating streaks."
Owing to the very rare atmosphere, the vapours, he thinks, would not ascend but would roll down the outsides of the craterlets and along the borders of the canals, thus irrigating the immediate vicinity and serving to promote the growth of some form of vegetation which renders the canals and oases visible. This opinion is especially important because, next to Mr. Lowell, Mr.
Similar craterlets occur on the rims of other great craters, forming ray-centres. The majority of the streaks appear to issue from one or more of these minute craters, which rarely exceed a mile in diameter. Kepler includes two such craterlets, but here the flow seems to have been more uniform over the edges of the whole crater, and is not distinctly divided up into separate streams.
Pickering is perhaps the astronomer who has given most attention to Mars during the last fifteen years. He was for some time at Flagstaff with Mr. Lowell, and it was he who discovered the oases or craterlets, and who originated the idea that we did not see the 'canals' themselves but only the vegetable growth on their borders.
W.H. Maw and others have detected many minute depressions in connection with these curious objects; and N. of them, on the outer slope of C, where it runs out to the level of the plateau, I have seen the surface at sunset riddled like a sieve with craterlets and little pits.
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