[Illustration: THREE-INCH TRANSIT, BY WARNER & SWASEY.]
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.”
[Illustration: CAROLUS LINNÆUS OF SWEDEN, FATHER OF MODERN BOTANY.
This illustration was prepared by a Swedish society, and represents the famous botanist after his return from the exploration of Lapland, and with a bunch of his favorite flower (_Linnæa borealis_) in his hand. ]
_Vice President Academy of Natural Sciences, Philadelphia_.
Botany, in its general sense, signifies the knowledge of plants. In the earlier periods of human history plants appealed to mankind as material for food or medicine; and down to comparatively recent times botanical studies were pursued mainly in these directions. Dioscorides, a Greek, who lived in the first century of the Christian era, is the earliest writer of whom we have knowledge that can lay a claim to botanical distinction, but the medical property of plants was evidently the chief incentive to his task. It was not until the beginning of the sixteenth century that botany, in its broad sense, became a study, and Le Cluse, a French physician, who died in 1609, may be regarded as one of its patriarchs. Still the medical uses of plants were steadily kept in view. The English botanist, John Gerarde, who was a contemporary of Le Cluse, or Clusius, as botanists usually call him, wrote a remarkable work on botany,—remarkable for his time,—but this was styled a “Herbal,” as were other famous botanical works down to the beginning of the present century.