THE SOLAR ECLIPSE OF MAY 6 TH, 1883. 247 
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 envel- 
oped 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 for millions of miles from the Sun. Accord- 
ing to Dr. Hasting's view it must be light from the Sun which has undergone 
refraction : /. e., 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 direc- 
tion of the object producing them by a line at right angles to the wave front. 
Now suppose a body is placed between the object producing the waves and the 
sensitive organ. The waves miist 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 atmos- 
phere, 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. 
To determine this point Dr. Hasting's 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. 
