Biog7'apMcal Memoir of Sir WilUam Hersclui. 13 



is for this reason, that, being placed in the interior of this nebu- 

 losity, we see it as a zone which divides and surrounds the hea- 

 vens. The first origin of these views occurs, if I mistake not, 

 in the writings of Kant, and afterwards in those of Lambert, 

 one of the most celebrated geometricians of Germany. But Her- 

 schel, to whom these works were unknown, did not confine 

 himself to general considerations. He deduced from positive 

 and multiplied observations that explanation, which had been 

 entertained by the celebrated philosopher of Koenigsberg, and 

 the academician of Berlin. 



He distinguishes among the nebulosities those which power- 

 ful telescopes resolve into a multitude of separate stars, those in 

 which one or more shining centres are observed, and those 

 which he names planetary, of a more defined spherical form, 

 and a more homogeneous lustre. He shews the sin<Tular varie- 

 ty of this order of phenomena, most of which were before un- 

 known. His catalogues contain more than two thousand nebu- 

 losities, some resembling the~ Milky- Way, others open in the 

 middle, and of an annular figure, but the greater part under the 

 most diversified and irregular forms. Lastly, He added a mul- 

 titude of observations to those that had already been made on 

 the stars which are coloured red, blue or green, or which pre- 

 sent shades of these colours, and principally on the double or 

 multiple stars. 



If one now considers the whole of these Pacts together, he na- 

 turally rises to the idea of a rare and diffuse luminous matter, 

 of which all the celestial bodies have been formed. This mat- 

 ter, diffused over every part of the universe, is very une- 

 qually condensed there. It is still in the state of vapour in 

 many nebulosities, and in the atmospheres of the comets, which 

 are so extended and so variable. The principle of gravitation 

 does not act on the bodies of the planetary system alon? ; it is 

 present in all points of space, and always opposed to the expan- 

 sive force of heat. It is conceived that universal attraction may 

 have gradually united these luminous vapours ; that the shining 

 centres, whether single or multiple, the groupes of stars, and the 

 solid bodies, are formed of them. These effects are not equally 

 sensible in the different stars ; they are much advanced in some, 

 very weak in otliers, and tend to manifest themselves more and 



