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Nature volume 81, pages 8283 (15 July 1909) | Download Citation



RADIAL MOTION IN SUN-SPOT VAPOURS.—Referring to some comments and queries, by Mr. Buss, in the May number, Mr. Evershed gives further details of the radial motion discovered in sun-spot vapours, in No. 411 Of the Observatory. He has found that when the slit of the spectroscope does not bisect the spot symmetrically, but crosses the penumbra on the side of the spot nearer to the centre of the sun's disc, the lines are always convex towards the violet; whereas if the slit crosses the opposite side of the penumbra they are convex towards the red. That the line displacements are due solely to motion is shown by the change in position angle of the maximum shift as the spot traverses the disc. The maximum displacement is always such as to indicate that the maximum motion is along the radius, but the observations are not yet sufficiently delicate to disprove the existence of a superimposed, relatively slow spiral motion; on the other hand, there is no direct evidence that such an outward spiral motion exists.

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