﻿234 Prof. W. A. Norton on the Corona seen 



that some individual jets will proceed in convex, and others in 

 concave curves, accordingly as the escaping matter is repelled or 

 attracted by the sun. 



2. Observations on the physical constitution of the corona with 

 the spectroscope and polaris cope. — The results of the observations 

 made at the late eclipse, with the spectroscope and polariscope, 

 are strongly confirmatory of the truth of the theory of the corona 

 under discussion. Professor Pickering, in the report of his 

 observations with a polariscope, says, " The form of polariscope 

 used was that adopted by Arago in his experiments on sky 

 polarization. It consists of a tube about 20 inches long and 

 2 inches in diameter, one end of which is closed by a double 

 image-prism of Iceland spar, and the other by a plate of quartz. 

 Looking through the former we see two images of the latter, 

 which, when the light is polarized, assumes complementary tints. 

 If, now, the corona was polarized in planes passing through 

 the centre of the sun (as is generally admitted) — when viewed 

 through the polariscope, in one image the upper and lower parts 

 should have appeared blue, and those on the right and left 

 yellow; while in the second image these colours would have been 

 reversed, the yellow being above and below, and the blue on the 

 sides. In reality the two images were precisely alike, and both 

 pure white ; but one was on a blue, and the other on a yellow 

 background. From this we infer that the corona was unpo- 

 larized, or, at least, that the polarization was too slight to be 

 perceptible." 



We may infer from this that the corona is either self-luminous 

 or shines by diffuse reflection, since specular reflection produces 

 polarization*. 



The testimony of the spectroscope is still more decisive. Profs. 

 Pickering, Harkness, and Young agree that the spectrum from 

 the light of the corona was a continuous one, or free from dark 

 lines, but containing one or more bright lines. The absence 

 of dark lines indicates that the corona did not shine by the light 

 of the photosphere, reflected either diffusely or specularly from 

 its substance ; since such light, after reflection, should, like the 

 direct solar light, have given a spectrum with the Fraunhofer 

 lines. The presence of bright lines, on the other hand, is a 

 direct indication that the corona was self-luminous, and there- 

 fore that its light was the result either of combustion or of 

 electric discharges. As it is hardly supposable that an actual 

 combustion could prevail at the distance of tens and hundreds 



"* The question whether the light from the corona is in any degree polar- 

 ized or not cannot be regarded as definitively settled. It is to be hoped 

 that the observations to be made on the eclipse of December will remove 

 all doubt on this point. 



