The immense distance of Uranus from our Earth, its small angular diameter, and the feebleness of its light, seemed to preclude the hope that, if it were attended by satellites of the same dimensions in proportion to its own magnitude as those of the satellites of Jupiter and Saturn in proportion to their magnitude, they could be descried by any human observer.  The patient, persevering, reverent temper of Herschel took no account, however, of any discouraging or unpropitious circumstances.  What he did was to substitute for telescopes of the ordinary construction the new and gigantic forty-foot tube already described; and, thus, with unremitting vigilance and intense zeal, he arrived at the discovery (between January 4, 1787, and February 28, 1794) of the six satellites of Uranus; in other words, he revealed to man the completeness of a new system,—­a system which will always be identified with his name.

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Those singular meteors, the comets, which flash through heaven with long trails of light, and of old astonished the nations as if they were harbingers of some overwhelming calamity, were also the frequent subjects of our astronomer’s investigations.  He brought some of his fine and powerful instruments to bear on a comet discovered by Mr. Pigott in 1807, and closely and carefully investigated its physical constitution.

The nucleus, or head, was circular and well determined, and evidently shone by its own light.  Very small stars seemed to grow pale, “to hide their diminished heads,” when seen through its coma or tail.  It is true, however, that this faintness may have been only apparent, and due to the circumstance of the stars being projected on a luminous background.  Such was Herschel’s explanation.  A gaseous medium, capable of absorbing sufficient solar radiance to efface the light of some “lesser stars,” appeared to him to possess in each stratum a sensible quantity of matter.  Hence it would cause a real diminution of the light transmitted, though nothing would indicate the existence of such a cause.[1]

[Footnote 1:  This conclusion is disputed by many astronomers.]

Herschel examined the beautiful comet of 1811 with equal accuracy.  “Large telescopes showed him, in the midst of the gaseous head, a rather reddish body of planetary appearance, which bore strong magnifying powers, and showed no sign of phase (that is, of change of aspect, as in the case of the Moon).  Hence Herschel concluded that it was self-luminous.  Yet, if we reflect that the planetary body under consideration was not a second in diameter, the absence of a phase,” says Arago, “does not appear a demonstrative argument.”

The same writer adds:—­