Page:Popular Science Monthly Volume 6.djvu/764

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THERE is little rest for the astronomers. Although their science is the oldest and exactest, and has long since taken its place as one of the most perfected divisions of knowledge, yet there never was a time of greater solicitude in regard to undetermined celestial questions than the present. New problems are presented of transcendent interest, and the progress in the construction of instruments and increasing experience in observation are certain to be rewarded with important extensions of astronomical knowledge.

And there is little rest for the astronomers, not only because of the urgent questions that have recently arisen in their science, but because many of the great phenomena in which they are interested are observable only at critical moments and at rare intervals, and only at a few points upon our planet. The present year will ever be memorable in astronomic annals because of the extensive preparations made to study the transit of Venus; but, while the various parties of observers are returning from the distant stations upon the globe where their observations were made, other expeditions have been fitted out which are traveling again to distant places to observe an eclipse of the sun. This is to take place on the 5th of April; is visible only in the Eastern Hemisphere, and will be mainly observed from stations in the kingdom of Siam. The shadow of total darkness will sweep rapidly along a line of about one hundred miles in breadth, and the time of total obscuration, when all the grand phenomena are displayed, will be but a few seconds more than four minutes. Yet within these fleeting moments many imposing effects are to be accurately noted which will serve as data for resolving the most important questions relating to the constitution of the sun. It was a splendid victory of scientific enterprise when Lockyer and Janssen showed that eclipses could be dispensed with in studying the solar prominences with the spectroscope, and that with their instruments they can at any time sweep round the solar outline, and watch and define those mighty eruptions of gaseous matter which rise to a height of tens and even hundreds of thousands of miles above the photosphere, or light-giving portion of the solar atmosphere; but these observations only heighten the interest of the grand effects which appear when the sun's disk is completely darkened. It is then impressively recognized that this great luminary is very far from being the clear-cut, sharply-defined, luminous globe that it seems to ordinary observation. Its ragged edge is stupendously mountainous, and there moreover stretches away a mighty upper atmosphere, or luminous appendage, called the corona, which can only be examined during the few precious moments of solar darkening.

The corona is therefore now the grand point of attack in a solar eclipse, by telescopic observation, photographic representation, and spectrum analysis; and, with each step of improvement in the construction of instruments, and the facility of their use, we are justified in expecting important accessions to our knowledge of that remarkable phenomenon.

The preparations for observing the April eclipse are suggestive of other considerations which should not be lost sight of. The interests of science are beginning to be recognized throughout the world, and to bring the most diverse nationalities into close relation upon a common platform of sympa-