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This work must, however, be regarded as merely introductory to the main labours of John Herschel's life. His father devoted the greater part of his years as an observer to what he called his "sweeps" of the heavens.
One of the best illustrations of Sir John Herschel's literary powers is to be found in the address which he delivered at the Royal Astronomical Society, on the occasion of presenting a medal to Mr. Francis Baily, in recognition of his catalogue of stars. The passage I shall here cite places in its proper aspect the true merit of the laborious duty involved in such a task as that which Mr.
Herschel's discovery established the interesting fact that, in certain of these double stars, or binary stars, as these particular objects are more expressively designated, there is an actual orbital revolution of a character similar to that which the earth performs around the sun.
To suggest that there was yet another world belonging to our system outside the path of the furthest known planet would have seemed to most people like pure folly. But in Herschel's day, nobody had ever heard of a new planet being discovered since the beginning of all things.
The luminary of Herschel's fancy could scarcely be more clearly portrayed; some added words, however, betray the origin of the Cardinal's idea. "The earth also," he says, "would appear as a shining star to any one outside the fiery element."
Got home to Herschel's while the sun yet shone, and I having the day before begged the favour of him to repeat for Fanny and Lestock the experiments and explanations on polarised light and periodical colours, he had everything ready, and very kindly went over it all again, and afterwards said to Mrs. Herschel, "It is delightful to explain these things to Mrs.
Is it not curious, that so vast a being as the whale should see the world through so small an eye, and hear the thunder through an ear which is smaller than a hare's? But if his eyes were broad as the lens of Herschel's great telescope; and his ears capacious as the porches of cathedrals; would that make him any longer of sight, or sharper of hearing? Not at all.
In this passage Darwin doubtless refers to a remark of Sir John Herschel's in his admirable "Preliminary Discourse on the Study of Natural Philosophy," a book which exercised a most remarkable and beneficial influence on the mind of the young naturalist.
With Sir John Herschel's survey of the Southern Hemisphere it may be said that his career as an observing astronomer came to a close. He did not again engage in any systematic telescopic research. But it must not be inferred from this statement that he desisted from active astronomical work.
Clearly the actual number of multiple stars is beyond all present estimate. The elder Herschel's early studies of double stars were undertaken in the hope that these objects might aid him in ascertaining the actual distance of a star, through measurement of its annual parallax that is to say, of the angle which the diameter of the earth's orbit would subtend as seen from the star.
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