To determine this point Dr. Hastings invented the following instrument: Two lozenge-shaped prisms of glass were fastened in the form of a letter V, and so arranged that all the light falling within the aperture of the V was lost, and that falling on the ends of the glass prisms was transmitted by a series of reflections to the apex of the V, where the prisms touched; here was placed a refracting prism, so that the light could be analyzed. This instrument was attached to the eye piece of the telescope, and the image of the eclipse reduced to such a size that the moon just fitted into the aperture of the V, while opposite sides of the corona were reflected through the prisms to the place where they came together. In this way both sides of the corona were seen through the eye-piece at the same time. On looking at the eclipse this is what Dr. Hastings saw: The light of the corona was divided into its constituents. Prominent among them was a bright green line, which is designated by the number 1,474; to this line attention was directed. Its presence in the spectrum has been an argument in favor of the view that the corona is a solar atmosphere. If this is the case, the line should remain fixed during the eclipse; but if the corona is due to diffraction, this line should change. It should grow shorter in the light from one side of the corona, and longer on the other. The observation was now reduced to watching for a change in the relative length of two green lines. At the beginning of totality the line from the west side was much the longer, but as the eclipse progressed it shortened notably, while the line from the east side, shorter by about one-third at the beginning of the eclipse, grew longer. When the eclipse ended, the proportions of the lines were exactly reversed. There had been a change equal to two-thirds the length of the lines, while the sun and moon had only changed their relative positions by an extremely small amount. The only way in which this phenomenon can be accounted for is on the diffraction theory. The material view of the corona will not answer for it. But there are other discrepancies in the older view which have been known for some time. The principal ones are: 1. It is known from study of the sun that the gaseous pressure at the surface must be less than an inch of mercury, and is probably less than one-tenth of an inch, but an atmosphere extending to the supposed limits would cause an enormous pressure at the sun's surface, especially since the force of gravity on the sun is very much greater than on the earth. 2. The laws of gravitation would require a solar atmosphere to be distributed symmetrically around the sun, while the corona is enormously irregular in form. The sun is irregular in outline, which would make its diffracted phenomena show the observed irregularity, but it is symmetrical as regards density. 3. The most interesting discrepancy of the theory of the solar atmosphere is the