Page:Popular Science Monthly Volume 41.djvu/276

264 looking at the corona through, screens of colored glass or other absorptive media had not been satisfactory. The author had therefore undertaken to use photography, and had satisfied himself that under certain conditions of exposure and development, a photographic plate could be made to record minute differences of illumination existing in different parts of a bright object, which was so subtle as to be at the very limit of the power of recognition of a trained eye, and even, perhaps, of those that surpassed that limit. Describing his apparatus and method, he showed that it was possible, by isolating through properly chosen absorbing media, the light of the sun in the violet part of the spectrum, to obtain photographs of the sun surrounded by an appearance distinctly coronal in its nature. He afterward found that, by using plates sensitive to violet light only, it was possible to do away with absorbing media and remove the difficulties that occurred in sifting the light. In 1886 Dr. Huggins accounted for his failure to obtain in England, since the summer of 1883, photographs showing satisfactory indications of the corona, by the existence in the atmosphere since the autumn of 1883 of finely divided matter which caused an abnormally large amount of glare. Mr. Ray Woods had met the same trouble in Switzerland in the summer of 1884.

In his British Association address, 1891, Prof. Huggins repeated a conclusion which he had expressed in 1885, that the corona is essentially a phenomenon similar in the cause of its formation to the tails of comets—consisting for the most part of matter going from the sun under the action of a force, possibly electrical, which varies as the surface, and can therefore in the case of highly attenuated matter easily master the force of gravity even near the sun—as according with the lines along which thought had been directed by the results of subsequent eclipses.

In the early part of 1868 Prof. Huggins presented to the Royal Society some observations on a small change of refrangibility which he had remarked in a line in the spectrum of Sirius as compared with a line of hydrogen, from which it appeared that the star was moving from the earth with a velocity of about twenty-five miles a second, if the probable advance of the sun in space were taken into account. The thought of discovering motion in this way was not wholly new, though Prof. Huggins was the first to apply it in practice. The Rev. John Mitchell, of the Royal Society, presented an ingenious paper, in 1783, On the Means of discovering the Distance, Magnitude, etc., of the Fixed Stars, in Consequence of the Diminution of the Velocity of their Light, in which he suggested that by the aid of a prism "we might be able to discover diminutions in the velocity of light as perhaps a