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 more valuable than copious and accurate knowledge of the proper motions of the stars. It seems from these discoveries at Potsdam and at Lick that we may now entertain a hope that abundant and accurate information of the character that I have indicated will be promptly forthcoming.

The researches of Professor Keeler at Lick have already afforded us some information with regard to the proper motions of the nebulæ in the line of sight. Here, indeed, an entirely new departure has been made. Most of these objects are so ill-defined that their position cannot be measured, or cannot by ordinary methods be even specified with the accuracy necessary for the determination of their proper motions. The vagueness of nebulæ is not, however, a bar to the application of the spectroscope in the measurement of its movements in the line of sight. We still know nothing as to the movements of nebulæ athwart that line. But it is something for us to have obtained information as to the progress of these bodies in one direction at all events. An attempt was made to solve this problem a good many years ago by Sir W. Huggins himself; but the apparatus that was then available did not possess the refinement necessary for measurements so delicate. The resources of the splendid equipment at Lick have provided what is required, and Prof. Keeler has ascertained the movements of some nebulæ. As an illustration of his results, we may take the famous nebula in Orion. He finds that this object is retreating from our system at the rate of about ten miles a second. The most rapid movement he has yet discovered in one of these nebulous objects is a pace of forty miles a second.