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of William Herschel.
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tion of the heavens. His classes were arranged with this end, and they are to-day adopted. They were:
| Class I. | "Bright nebulæ (288 in all).
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| II. | "Faint nebulæ (909 in all).
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| III. | "Very faint nebulæ (984 in all).
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| IV. | "Planetary nebulæ, stars with burs, with milky chevelure, with short rays, remarkable shapes, etc. (79 in all).
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| V. | "Very large nebulæ (52 in all).
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| VI. | "Very compressed and rich clusters of stars (42 in all).
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| VII. | "Pretty much compressed clusters (67 in all).
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| VIII. | "Coarsely scattered clusters of stars" (88 in all).
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The lists of these classes were the storehouses of rich material from which Herschel drew the examples by which his later opinions on the physical conditions of nebulous matter were enforced.
As the nebulæ were discovered and classi-
