Pagina:Scientia - Vol. VII.djvu/9

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At the request of the Editor of Scientia, I send a summary of the state of our present knowledge about the planet Mars from the work of the Lowell Observatory. I shall refer to the various facts by numerals, and thus, from their succinctness, give the reader an easy opportunity of estimating their concurrent force and of the conclusion to which they lead.

1. Mars turns on its axis in 24 hours 37 minutes 22.65 seconds. This makes its day about forty minutes longer than ours.
2. The latest determination of the position of that axis, determined at this Observatory from all the best observations up to 1905, gave for its tilt to the plane of the planet’s orbit, 24.° This determination has been incorporated in the British Nautical Almanac. Such a tilt causes seasons almost the counterpart of our own, except that orbital excentricity opportions them differently.
3. Its year consists of 687 of our days, 669 of its own.
4. It shows polar caps which melt in the Martian summer and form again in the Martian winter.
5. The making cap is of indefinite contour. It is a misty white, merging gradually into the surrounding land.
6. The melting cap, on the other hand, is bordered by a blue belt which retreats with the cap. This shows it to be the product of the disintegration of the cap. The fact excludes the possibility of its being formed of carbon dioxide, because that substance at pressures of one atmosphere or less, such as exist on Mars, passes at once from the solid to the gaseous