At the earlier periods of Herschel’s observations, that illustrious observer appears to have inclined to the belief that all nebulæ were but remote clusters of stars, so distant, so faint, and so thickly agglomerated as to affect the eye only by their combined luminosity, and at this period of the nebular history it was supposed that increased telescopic power would resolve them into their component stars. But the familiarity which Herschel gained with the phases of the multitudinous nebulæ that passed in review before his eyes, led him ultimately to adopt the opinion, advanced by previous philosophers, that they were composed of some vapoury or elementary matter out of which, by the process of condensation, the heavenly bodies were formed; and this led him to attempt a classification of the known nebulæ into a cosmical arrangement, in which, regarding a chaotic mass of vapoury matter as the primordial state of existence, he arranged them into a series of stages of progressive development, the individuals of one class being so nearly allied to those in the next that, to use his own expression, not so much difference existed between them “as there would be in an annual description of the human figure were it given from the birth of a child till he comes to be a man in his prime.” (_Philosophical Transactions, Vol. CI., pp. 271_, _et seq._) His category comprises upwards of thirty classes or stages of progression, the titles of a few of which we insert here to illustrate the completeness of his scheme. Class 1. Of extensive diffused nebulosity. (A table of 52 patches of such nebulosity actually observed is given, some of which extend over an area of five or six square degrees, and one of which occupies nine square degrees.) ” 6. Of milky nebulosity with condensation. ” 15. Of nebulæ that are of an irregular figure. ” 17. Of round nebulæ. ” 20. Of nebulæ that are gradually brighter in the middle. ” 25. Of nebulæ that have a nucleus. ” 29. Of nebulæ that draw progressively towards a period of final condensation. ” 30. Of planetary nebulæ. ” 33. Of stellar nebulæ nearly approaching the appearance of stars.