Pagina:Scientia - Vol. VII.djvu/259

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the origin and nature of comets 251

much smaller than those suggested by Prof. Schaeberle. Mr Burns («Journal Brit. Astron. Assoc.», XIX, 5) says. «The radiant matter emitted by the sun is identical with the Beta rays given off by radium.... The impact of this radiant matter on the meteorites composing the comet’s head generates light, and the spectrum of this light will be that of the atmosphere surrounding the meteorites.... We can account for the formation of the tail by the known property possessed by radiant matter of acting as nuclei for the condensation of molecular aggregates. I suppose that as the particles of radiant matter from the sun pass through the head of a comet they collect matter round them, and become of sufficient size to reflect light. And Prof. Newall wrote in the «Monthly Notices» for Feb. 1909 «Is anyone who is familiar with the phenomena and theory of comet’s tails prepared to say that the repulsion of these tails is not simply a phenomenon indicating the existence of this constant radial outstreaming of dust, rendered manifest by the glowing of the vapours set free by the nucleus of the comet, possibly under the influence of the incessant bombardment by the dust?» It is rather remarkable that these two passages were written simultaneously, Mr Burns knowing nothing of Prof. Newall’s view. The idea of the bombardment by ultramicroscopical particles ejected from the sun is coming more and more to the fore to explain various phenomena in the solar system, in particular the corona, the aurora, and magnetic storms. In connection with the last, I recall Mr Maunder’s papers in the Monthly Notices, in which he showed that the matter supposed to produce the storms was not projected equally from the sun in all directions, but from definite areas in the sun (frequently marked by some notable spot or other disturbance) and outwards along definite streamlines, like the jet of water from a fireman’s hose. For this reason I am not inclined to attribute the whole of the tail-phenomena of comets to this action, though I think it would be decidedly rash at the present time to deny its connection with special outbursts, such as those exhibited by Morehouse’s comet, of which Mr Eddington said «I am not sure that the exceptional activity of this comet is not due to the physical state of the sun at the time, rather than to the constitution of the object itself».