75 6 THE POPULAR SCIENCE MONTHLY. 



aerial ocean necessarily conceals from ns by overpowering them any 

 sources of light less brilliant than itself which are in the heavens be- 

 yond. From this cause the stars are invisible at midday. This illu- 

 minated air also conceals from us certain surroundings and appendages 

 of the sun, which become visible on the very rare occasions when the 

 moon coming between us and the sun cuts off the sun's light from 

 the air where the eclipse is total, and so allows the observer to see the 

 surroundings of the sun through the cone of unilluminated air which 

 is in shadow. It is only when the aerial curtain of light is thus with- 

 drawn that we can become spectators of what is taking place on the 

 stage beyond. The magnificent scene never lasts more than a few 

 minutes, for the moon passes and the curtain of light is again before 

 us. On an average, once in two years this curtain of light is lifted 

 for from three to six minutes. I need not say how difficult it is from 

 these glimpses at long intervals even to guess at the plot of the drama 

 which is being played out about the sun. 



The purpose of this discourse is to describe a method by which it 

 is possible to overcome the barrier presented to our view by the bright 

 screen of air, and so watch from day to day the changing scenes tak- 

 ing place behind it in the sun's surroundings. 



The object of our quest is to be found in the glory of radiant 

 beams and bright streamers intersected by darker rifts which appears 

 about the sun at a total solar eclipse. The corona possesses a struct- 

 ure of great complexity, which is the more puzzling in its intricate 

 arrangement because, though we seem to have a flat surface before us, 

 it exists really in three dimensions. If we were dwellers in Flatland 

 and the corona were a sort of glorified catherine-wheel, the task of 

 interpretation would seem less difficult. But, as we are looking at an 

 object having thickness as well as extension, the forms seen in the 

 corona must appear to us more or less modified by the effect of per- 

 spective. This consideration tells us also that the intrinsic brightness 

 of the corona toward the sun's limb is much less than its apparent 

 brightness as seen by us, of which no inconsiderable part must be due 

 to the greater extent of corona in the line of sight as the sun is ap- 

 proached. The corona undergoes great and probably continual change, 

 as the same coronal forms are not present at different eclipses. 



The attempts which have been made from time to time to see the 

 corona without an eclipse have been based mainly upon the hope that 

 if the eye were protected from the intense direct light of the sun, and 

 from all light other than that from the sky immediately about the 

 sun, then the eye might become sufficiently sensitive to perceive the 

 corona. These attempts have failed because it was not possible to 

 place the artificial screen where the moon comes, outside our atmos- 

 phere, and so keep in shadow the part of the air through which the 

 observer looks. The latest attempts have been made by Professor 

 Langley at Mount Whitney, and Dr. Copeland, assistant to Lord 



