385. _Structure of the Nubeculæ._--Fig. 455 shows the structure of these clouds as revealed by a powerful telescope. The general ground of both consists of large tracts and patches of nebulosity in every stage of resolution,--from that which is irresolvable with eighteen inches of reflecting aperture, up to perfectly separated stars, like the Milky-Way and clustering groups. There are also nebulæ in abundance, both regular and irregular, globular clusters in every state of condensation, and objects of a nebulous character quite peculiar, and unlike any thing in other regions of the heavens. In the area occupied by the _nubecula major_ two hundred and seventy-eight nebulæ and clusters have been enumerated, besides fifty or sixty outliers, which ought certainly to be reckoned as its appendages, being about six and a half per square degree; which very far exceeds the average of any other part of the nebulous heavens. In the _nubecula minor_ the concentration of such objects is less, though still very striking. The nubeculæ, then, combine, each within its own area, characters which in the rest of the heavens are no less strikingly separated; namely, those of the galactic and the nebular system. Globular clusters (except in one region of small extent) and nebulæ of regular elliptic forms are comparatively rare in the Milky-Way, and are found congregated in the greatest abundance in a part of the heavens the most remote possible from that circle; whereas in the nubeculæ they are indiscriminately mixed with the general starry ground, and with irregular though small nebulæ. THE NEBULAR HYPOTHESIS. 386. _The Basis of the Nebular Hypothesis._--We have seen that the planets all revolve around the sun from west to east in nearly the same plane, and that the sun rotates on his axis from west to east. The planets, so far as known, rotate on their axes from west to east; and all the moons, except those of Uranus and Neptune, revolve around their planets from west to east. These common features in the motion of the sun, moons, and planets, point to the conclusion that they are of a common origin. 387. _Kant's Hypothesis._--Kant, the celebrated German philosopher, seems to have the best right to be regarded as the founder of the modern nebular hypothesis. His reasoning has been concisely stated thus: "Examining the solar system, we find two remarkable features presented to our consideration. One is, that six planets and nine satellites [the entire number then known] move around the sun in circles, not only in the same direction in which the sun himself revolves on his axis, but very nearly in the same plane. This common feature of the motion of so many bodies could not by any reasonable possibility have been a result of chance: we are therefore forced to believe that it must be the result of some common cause originally acting on all the planets.