Astronomical discovery . SEPT. 20, NOW 13, 190:. IX.— rduxd Xova Persei. {Frjiu fl:otog)\ipJis fake:: at the Yokc^ Oy C. II. Riicluy 1 ACCIDENTAL DISCOVERIES 147 graphs at intervals, it was found that this nebulosity itswas rapidly changing in shape. Eapidly is, of ^^^*course, a relative term, and a casual inspectionof two of the photographs might not convey anyimpression of rapidity ; it is only v^hen we cometo consider the enormous distance at which themovements, or apparent movements, of the nebulsemust be taking place that it becomes clear howrapid the change

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Astronomical discovery . SEPT. 20, NOW 13, 190:. IX.— rduxd Xova Persei. {Frjiu fl:otog)\ipJis fake:: at the Yokc^ Oy C. II. Riicluy 1 ACCIDENTAL DISCOVERIES 147 graphs at intervals, it was found that this nebulosity itswas rapidly changing in shape. Eapidly is, of ^^^*course, a relative term, and a casual inspectionof two of the photographs might not convey anyimpression of rapidity ; it is only v^hen we cometo consider the enormous distance at which themovements, or apparent movements, of the nebulsemust be taking place that it becomes clear howrapid the changes must be. It was not possibleto determine this distance with any exactness,but limits to it could be set, and it seemed pro-bable that the velocity of the movement wascomparable with that of light. The conclusionsuggested itself that the velocity might actuallybe identical with that of light, in which case whatwe saw was not the movement of actual matter, Due tobut merely that of illumination, travelling from Jfi^mlna-^point to point

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Keywords: ., bookcentury1900, bookdecade1900, booksubjectastronomy, bookyear19