ABSTRACT
The value of Mars in the history of astronomy is very great. It is impossible to conjecture how much longer the world would have had to wait for the laws of motion enunciated by Kepler but for the considerable eccentricity of the orbit of Mars, which was sufficient to preclude the possibility of a circular orbit. The spectroscope in recent years shows an almost total absence of water absorption, though traces have been noted by Huggins and Vogel. The melting of the 'polar caps' which sometimes is complete, a very different state of things to that which obtains on the earth, seems to point to a temperature far higher than the theoretical mean temperature. It would seem possible that the so-called 'theoretical' temperature, deduced from the distance and albedo of Mars, is absolutely unreliable, and that, owing to the relative preponderance of carbonic acid instead of water vapour, Mars may retain comparatively more heat than the earth.
