Typical stages in development of a solar system. (Reproduced from nature. See Chapter XIII.)—1. Newton’s comet, A.D. 1680. 2. Comet of 1811, from Guillemin. 3. Donati’s comet, 1858, from Proctor. 4. Nebula in ship Argo, from Flammarion. 5. Open spiral nebula in Virgo, Plate XV., Nichol’s “Architecture of the Heavens,” after Lord Rosse. 6. Plate XII. of same work, nebula in Canes Venatici: a partially closed spiral. 7. Frontispiece of same, an almost completed spiral, in the Lion, seen obliquely: rupture of convolutions preparatory to formation of planets. 8. Ideal solar system.