When, in 1877, Professor Hall, through the powerful telescope at Washington, saw that Mars was attended by two tiny satellites, he put a permanent injunction on the further use of the once favorite phrase,
“The snowy poles of moonless Mars.”
And so of the question oft discussed in the old-time debating societies, “Are the planets inhabited?” It may still be left in the hands of young collegians, notwithstanding the fact that our largest telescopes give only negative testimony.
In a solar eclipse in February, 1736, that was annular in shape, just before the sun was completely hidden, the narrow horn of light seemed to break into a series of dots, or luminous points, which, when noted again a century later and described by Francis Baily, received the name of “Baily Beads.” It was attempted to explain this as caused by the moon’s mountains cutting off the last rays of sunlight, or else as produced by irradiation. But with the advent of stronger telescopic power the phenomenon has come to an end.
David Rittenhouse, of Norristown, whom Thomas Jefferson considered “second to no astronomer living,” built an orrery worth a thousand dollars, to illustrate mechanically the motions of all the planets, and though the instrument is still treasured in the University of Pennsylvania, and its duplicate at Princeton, among the relics of a past age, it is assigned to the category of toys. Mural circles, much depended upon to measure the declination of heavenly bodies, have fallen into disuse, supplanted by improved transit instruments.
THREE-INCH TRANSIT, BY WARNER & SWASEY.
XVI. PROBLEMS FOR FUTURE STUDY.
Many problems are in store for the future. The field for research still opens wide. How the solar activity is to be maintained was answered by Newton in the suggestion that comets falling into it kept up its supply of matter and energy. Waterston, in 1853, propounded the thought that meteoric matter may be the aliment of the sun. Now the prevalent theory is that a contraction of the sun’s volume, constantly in progress, but so slight as to be invisible to the most powerful telescope, is competent to furnish a heat supply equal to all that can have been emitted during historic periods.
Professor Newcomb answers the question, “How long will the sun endure?” by saying, “The physical conclusion to which we are led by a study of the laws of nature is that the sun, like a living being, must have a birth and will have an end. From the known amount of heat which it radiates we can, even in a rude way, calculate the probable length of its life. From fifteen to twenty millions of years seems to be the limit of its age in the past, and it may exist a few millions of years, perhaps five or ten, in the future.”