TEE SUN'S CORONA AND EIS SPOTS. 



549 



thing annular in its structure ; it appeared to me 

 to resemble, with some irregularities (as I stated 

 in 1851), the ornament round a compass-card. 

 Bruhns, of Leipsic, noted that the corona shone 

 with an intense white light, so lustrous as to dim 

 the protuberances." 



He noticed that a ray shot out to a distance of 

 about one degree, indicating a distance of at 

 least 1,500,000 miles from the sun's surface. 

 This was unquestionably a coronal appendage, as 

 neither the direction nor the length of the ray 

 varied for ten seconds, during which Bruhns di- 

 rected his attention to it. Its light was consid- 

 erably feebler than that of the corona, which was 

 of a glowing white, and seemed to coruscate or 

 twinkle. Bruhns assigned to the inner corona a 

 height varying from about 40,000 to about 80,000 

 miles. But this was unquestionably far short of 

 the true height. In fact, Secchi's photographs 

 show the corona extending to a distance of at 

 least 175,000 miles from the surface of the sun. 

 Therefore probably what Bruhns calls the base 

 of the corona was in reality only the prominence 

 region, and the inner corona was that which he 

 describes as varying in breadth or height from 

 near'.y one-half to a quarter of a degree — that is, 

 from about 800,000 to about 400,000 miles. De 

 La Rue gives a somewhat similar general descrip- 

 tion of the corona seen in 1860. He remarks 

 that it was extremely bright near the moon's 

 body, and of a silvery whiteness. The picture 

 of the corona by Feilitsch (given at page 343 of 

 my book on the Sun) accords with these de- 

 scriptions. 



On the whole, the eclipse of 1860 affords evi- 

 dence according well with the theory we have 

 been considering, except as regards the bright- 

 ness and the color of the corona, which corre- 

 spond more closely with what was observed last 

 July than with the lustre and color of the corona 

 in 1870 and 1871. In this respect, it is singular 

 that the eclipse of 1867, which occurred (see pre- 

 ceding note) when the sun-spots were fewest in 

 number, presented a decided contrast to that of 

 I860 — the contrast being, however, precisely the 

 reverse of that which our theory would require, 

 if the color and brightness of the corona be con- 

 sidered essential features of any law of association. 



Herr Grosch, describing the corona of 1867, 

 says, " There appeared around the moon a red- 

 dish, glimmering light, similar to that of the 

 aurora, and almost simultaneously with this (I 

 mean very shortly after it) the corona." It is 

 clear, however, from what follows, that the red- 

 dish light was what is now commonly called the 



inner corona, which, last July, when the sun was 

 in almost exactly the same condition as regards 

 the spots, was pearly white and intensely bright. 

 "This reddish glimmer," he proceeds, "which 

 surrounded the moon with a border of the breadth 

 of at most five minutes " (about 140,000 miles) 

 " was not sharply bounded in any part, but was 

 extremely diffused and less distinct in the neigh- 

 borhood of the poles." Of the outer corona he 

 remarks that — 



" its apparent height amounted to about 2S0,000 

 miles opposite the solar poles, but opposite the 

 bolar equator to about 670,000 miles. Its light was 

 white. This white light was not in the least ra- 

 diated itself, but it had the appearance of rays 

 penetrating through it ; or rather, as if rays ran 

 over it, forming symmetrical pencils diverging 

 outward and passing far beyond the boundary of 

 the white light. These rays had a more bluish 

 appearance, and might best be compared to those 

 produced by a great electro-magnetic light. Their 

 similarity to these, indeed, was so striking, that 

 under other circumstances I should have taken 

 them for such, shining at a great distance. The 

 view of the corona I have described is that seen 

 with the naked eye. ... In the white light of 

 the corona, close upon the moon's edge, there ap- 

 peared several dark curves. They were symmetri- 

 cally arched toward the east and west, sharply 

 drawn, and resembling in tint lines drawn with a 

 lead-pencil upon white paper. . . . Beginning at 

 a distance of one minute (about 26,000 miles), they 

 could be traced up to a distance of about nine 

 minutes (some 236,000 miles) from the moon's 

 edge." 



Almost all the features observed in this case 

 correspond closely with those noted and photo- 

 graphed during the eclipse of December, 1871. 

 In other words, the corona seen in 1867, when 

 the sun was passing through the period of least 

 solar disturbance, closely resembled the corona 

 seen in 1871, when the sun was nearly in its 

 stage of greatest disturbance. Even the spectro- 

 scopic evidence obtained in 1S71 and last July 

 may be so extended as to show with extreme 

 probability what would have been seen in 1867 

 if spectroscopic analysis had then been applied. 

 We cannot doubt that the reddish inner corona, 

 extending to a height of about 140,000 miles, 

 would have been found under spectroscopic anal- 

 ysis to shine in part with the light of glowing 

 hydrogen, as the reddish corona of 1871 did. 

 The white corona of last July, on the contrary, 

 shone only with such light as comes from glow- 

 ing solid or liquid matter. Here then, again, the 

 evidence is unfavorable to our theory ; for the 



