552 



THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



ring at all at the beginning of totality. In oth- 

 er words, so faint is the light of the gaseous 

 corona, even at its brightest part, close to the 

 sun, that the faint residual atmospheric light 

 which illuminates the sky over the eclipsed sun 

 at the beginning of totality sufficed to obliterate 

 this part of the coronal light. 



Whether, with any combination specially di- 

 rected to meet the difficulties of this observa- 

 tion, the gaseous corona can be rendered dis- 

 cernible, remains to be seen. I must confess 

 my own hopes that the problem will ever be suc- 

 cessfully dealt with are very slight, though not 

 absolutely evanescent. It seems to me barely 

 possible that the problem might be successfully 

 attacked in the following way: Using a tele- 

 scope of small size, for the larger the telescope 

 the fainter is the image (because of greater loss 

 of light by absorption), let the image of the sun 

 be received in a small, perfectly-darkened cam- 

 era attached to the eye-end of the telescope. 

 Now, if the image of the sun were received on a 

 smooth white surface, we know that the promi- 

 nences and the corona would not be visible. 

 And, again, if the part of such a surface on 

 which the image of the sun itself fell were ex- 

 actly removed, we know (the experiment has 

 been tried by Airy) that the prominences would 

 not be seen on the ring of white surface left 

 after such excision : still less, then, would the 

 much fainter image of the corona be seen. But 

 if this ring of white surface, illuminated in real- 

 ity by the sky, by the ring of prominences and 

 sierra, and by the corona, were examined through 

 a battery of prisms (used without a slit) adjusted 

 to any one of the known prominence tints, the 

 ring of prominences and sierra would be seen in 

 that special tint. If the battery of prisms were 

 sufficiently effective, and the tint were one of the 

 hydrogen-tints — preferably, perhaps, the red — 

 we might possibly be able to trace the faint im- 

 age of the corona in that tint. But we should 

 have a better chance with the green tint corre- 



sponding to the spectral line 1474 Kirchhoff. If 

 the ring of white surface were replaced by a 

 ring of green surface, the tint being as nearly 

 that of 1474 Kirchhoff as possible, the chance 

 of seeing the coronal ring in that tint would be 

 somewhat increased ; and still further, perhaps, 

 if the field of view were examined through green 

 glass of the same tint. It seems just possible 

 that if prisms of triple height were used, through 

 which the rays were carried three times, by an 

 obvious modification of the usual arrangement 

 for altering the level of the rays, thus giving a 

 power of eighteen flint-glass prisms of sixty de- 

 grees each, evidence, though slight, perhaps, 

 might be obtained of the presence of the sub- 

 stance which produces the green line. Thus va- 

 riations in the condition of the corona might be 

 recognized, and any law affecting such variations 

 might be detected. I must confess, however, 

 that a consideration of the optical relations in- 

 volved in the problem leads me to regard the 

 attempt to recognize any traces of the corona 

 when the sun is not eclipsed as almost hopeless. 

 It is clear that until some method for thus 

 observing the corona has been devised, future 

 eclipse observations will acquire a new interest, 

 from the light which they may throw on the co- 

 ronal variations and their possible association in 

 some way, not as yet detected, with the sun-spot 

 period. Even when a method has been devised 

 for observing the gaseous corona, the corona 

 whose light comes either directly or by reflec- 

 tion from solid or liquid matter will still remain 

 undiscernible except during total eclipses of the 

 sun. Many years, then, must pass before the 

 relation of the corona to the prominences and 

 the sun-spots shall be fully recognized. But 

 there can be no question that the solution of 

 this problem will be well worth waiting for, even 

 though it should not lead up (as it most probably 

 will) to the solution of the mystery of the peri- 

 odic changes which affect the surface of the sun. 

 — Contemporary Review. 



PARASITES AND THEIR DEVELOPMENT. 



By ANDREW WILSON. 



IF man is to be regarded as the favored child 

 of Nature, and if it be held as true that life 

 at large is subservient to his sway and rule, it is 

 no less true that he is liable to suffer severely 



from the attack of certain of his lower neighbors, 

 and that he is despoiled in various fashions by 

 some of the most insignificant of living beings. 

 Insects of various kinds, insignificant as to size, 



