Page:Sir William Herschel, his life and works (1881).djvu/232

210 of his views must be gained from the extended memoirs themselves. Here only the merest outline can be given.

In 1802 there is a marshaling of the various objects beyond our solar system. The stars themselves may be insulated, or may belong to binary or multiple systems, to clusters and groups, or to grand groups like the Milky Way. Nebulæ may have any of the forms which have been described; and, in 1811, he gives examples of immense spaces in the sky covered with diffused and very faint nebulosity. "Its abundance exceeds all imagination." These masses of nebular matter are the seats of attracting forces, and these forces must produce condensation. When a nebula has more than one preponderating seat of attracting matter, it may in time be, divided, and the double nebulæ have