Clinching this conclusion is the result of a search by Perrine for traces of the nebula on earlier plates. For on one taken by him on March 29 (1901) he found the process already started in two close coils, its conception thus clearly dating from the time of the star’s outburst. In Nova Persei, then, we actually witnessed a spiral nebula evolved from a disrupted star. What was this ejectum and what drove it forth? Professor Very regarded it as composed of corpuscles such as give rise to cathode rays discharged from the star under the stress of light pressure or electric repulsion. But I think we may see in it something simpler still; to wit, gaseous molecules driven off by light pressure alone—the smoke, as one may say, of the catastrophe—akin exactly to the constituents of comet’s tails. The mere light of the conflagration pushed the hydrogen molecules away. This would explain their presence and their exceeding hurry at the same time. They were started on their travels by domestic jars and kept going by the vivid after-effects of that infelicity. The fairly steady rate of regression from the nova observed may be explained by the observed decrease in the light of the repellent source. Such combined with the retarding effect of gravity might make the regression equable. This is the more explanatory as the speed was certainly much less than that of light, though greatly exceeding any possible from the direct disruption. At the same time both the bright and the dark lines of hydrogen seen in the spectrum stand accounted for; the colliding molecules, at their starting on their travels from the star, shining through their sparser fellows farther out. An interesting biograph of the levity of light! Nova Persei thus introduces us at its birth to one of a class of most interesting objects comparatively recently discovered and of most pregnant import,—the spiral nebulæ. [Illustration: GREAT NEBULA IN ORION—AFTER RITCHEY.] [Illustration: GREAT NEBULA IN ANDROMEDA—AFTER RITCHEY.] [Illustration: NEBULA M. 100 COMÆ—AFTER ROBERTS.]