From his observation during the eclipse of 1878, made at Central City, Dr. Hastings conceived the first idea of this explanation of the solar corona. Further study served to convince him of the truth of this theory, but he had no means of proving it. Before the present eclipse, however, he devised a crucial test of his theory. This test is based on the following already known phenomena: When the moon covers the face of the sun, an envelope of light is seen all round it; the envelope is not visible when the sun is shining, on account of the sun's greater brightness; this light is called the corona; it is extremely irregular in outline. According to the drawing of Mr. J. E. Keeler at the eclipse of 1878, it enveloped the sun as a hazy glow, extending for a distance of several minutes of arc from the sun's limb and at two nearly opposite points is extended out in two long streamers feathering off into space. The opinion has been that this light was due to an atmosphere extending millions of miles from the sun. According to Dr. Hastings' view, it must be light from the sun which has undergone refraction, i.e., which has been bent from its regular course by the interposition of an opaque body like the moon. In order to make this perfectly plain, suppose the front of a surface of waves of any sort to be striking an object which resists them. If an organ of sense is placed in the resisting object, it will judge the direction of the waves or the direction of the object producing them by a line at right angles with the wave front. Now suppose a body is placed between the body producing the waves and the sensitive organ. The waves must go around this body and will produce an eddy behind it, so that the wave front will have a different direction, and the organ of sense will conceive the origin of the waves to lie in a direction different from that before the body was interposed. Now consider the waves to be waves of light, and their origin the sun. The organ of sense is the retina of the eye. The moon is the opaque body interposed in the course of the waves, and they, being bent, make the impression on the eye that the light comes from beyond the edge of the sun. The moon covers the sun during the eclipse and a little more, so that it can move for about five minutes and still cover the sun entirely. This movement is very slight, and if the corona consists of light from a solar atmosphere, it should not change at all during this movement of the moon. But if diffraction is the cause of the light, then the slightest change in the relative positions of the sun and the moon should change the configuration of the corona, i.e., the corona should not remain exactly the same during a total eclipse. The character of the light as shown by a spectrum analysis should change.