Page:Popular Science Monthly Volume 4.djvu/54

44 reason to believe that the series stops just where our power of tracing it ceases; on the contrary, since the series is continuous as far as it goes, and since our own solar system is constituted as if it belonged to the series prolonged far beyond the limits which telescopic scrutiny has reached, we have reason for believing that such is indeed the interpretation of the observed facts. In other words, we may not unreasonably regard our solar system as a multiple system, a double star at certain ranges of distance, whence only the sun and Jupiter could be seen; a triple star at distances whence Saturn could be seen; and a quintuple star where Uranus and Neptune would come into view. To show what excellent reason exists for regarding Mercury, Venus, the Earth, and Mars, as not to be included in this view, it is only necessary to remark that not one of these planets could be seen until the limits of the solar system had been crossed. To eyesight such as ours, not one of the four terrestrial planets could be seen from Saturn, and still less, of course, from Uranus or Neptune. It would be as unreasonable to hold the ring of asteroids, or even the myriads of systems of meteorolites and aërolites, to be bodies resembling the earth and her fellow-terrestrial planets, as it is to hold these terrestrial planets to be bodies resembling Jupiter and his fellow-giants.

In all characteristics yet recognized by astronomers, Jupiter and Saturn differ most markedly from the earth and her fellow-planets. In bulk and mass they belong manifestly to a different order of created things; in density they differ more from the earth than the sun does; they rotate much more swiftly on their axes; they receive much less light and heat from the sun; the lengths of their year exceed the length of the earth's year as remarkably as their day falls short of hers; the atmospheric envelope of each is divided into variable belts, utterly unlike any thing existing in the earth's atmosphere; and, lastly, each is the centre of an important subsidiary scheme of bodies quite unlike the moon (the only secondary planet in the terrestrial family) as respects their relations to the primary around which they travel.

Notwithstanding all these circumstances in evidence of utter dissimilarity, and the fact that not one circumstance in the condition of the major planets suggests resemblance to the terrestrial planets, astronomy continues to treat of the planets of the solar system as though they formed a single family. It would appear as though the teachings of the astronomers who lived before the telescope was invented had so strong an inherent vitality, that more than two centuries and a half of discoveries adverse to those teachings are powerless to dispossess them of their authority. For no other reason can be suggested, as it appears to me, for the complete disregard with which the most striking characteristics of the major planets have been treated by modern astronomers.

If we consider one feature alone of those which have been just