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THE POPULAR SCIEXCE MONTHLY.— SUPPLEMENT. 



hundred cases of agreement would do in the way 

 of confirming it. 



In 1724 Maraldi noticed that the corona was 

 broadest first on the side toward which the moon 

 was advancing, and afterward on the side which 

 the moon was leaving. From this we may infer 

 that the corona was only a narrow ring on that 

 occasion, since otherwise the slight difference of 

 breadth due to the moon's eccentric position at 

 the beginning and end of totality would not have 

 been noticeable. Now, the year 1723 was one 

 of minimum disturbance, with one year of doubt 

 either way. Thus 172-f was certainly a year of 

 few sun-spots, and may have been the actual 

 year of minimum disturbance. The corona then 

 presented an appearance according with the the- 

 ory we are considering. 



Few eclipses have been better observed than 

 that of the year 1733. The Royal Society of 

 Sweden invited all that could spare the time to 

 assist, as far as their ability permitted, in record- 

 ing the phenomena presented during totality. The 

 pastor of Smoland states that at Catherinesholm 

 there was a ring around the sun about 70,000 

 miles in height. (Of course, these are not his 

 exact words ; what he actually stated was, that 

 the ring was about a digit in breadth.) This is 

 the exact height assigned to the coronal ring by 

 the observers of the eclipse of last July. The 

 ring seemed to be of a reddish color. Another 

 clergyman, Vallerius, states also that the ring 

 was of this color, but adds that at a consider- 

 able distance from the sun it had a greenish hue. 

 This suggests the idea that the outer corona was 

 seen also by Vallerius, and that it had consider- 

 able breadth. The reddish color of the inner 

 bright portion would correspond to the color it 

 would have if it consisted in the main of glow- 

 ing hydrogen. If that really was its constitu- 

 tion, then the theory advanced by one observer 

 of the recent eclipse, that at the time of mini- 

 mum solar disturbance the glowing hydrogen is 

 withdrawn from the corona, would be shown to 

 be incorrect. For 1733 was the actual year of 

 minimum solar disturbance. The pastor of Smo- 

 land states that, " during the total obscuration, 

 the edge of the moon's disk resembled gilded 

 . brass, and the faint ring round it emitted rays in 

 an upward as well as in a downward direction, 

 similar to those seen beneath the sun when a 

 shower of rain is impending." The mathemati- 

 cal lecturer of the Academy of Carlstad, M. 

 Edstrom, observed these rays with special at- 

 tention: he says that "they plainly maintained 

 the same position, until they vanished along with 



the ring upon the reappearance of the sun." On 

 the other hand, at Linkoping no rays were seen. 

 On the whole, it seems clear, from the accounts 

 of this eclipse/that the inner corona was bright 

 and narrow ; rays issued from the outer faint 

 ring ; but they were very delicate phenomena, 

 easily concealed by atmospheric haze, and thus 

 were not everywhere observed. As rays were 

 seen last July, there is nothing in the evidence 

 afforded by the eclipse of 1733, occurring at a 

 time of few spots, which opposes itself definitely 

 to the theory we are considering. But the red- 

 dish color of the corona, as already noticed, is a 

 doubtful feature : last July the bright inner coro- 

 na was of a pearly color. 



During the eclipse of February, 1766, the 

 corona presented four luminous expansions, and 

 seems to have had a greater extension than we 

 should expect in a year of minimum solar dis- 

 turbance. Such, however, the year 1766 cer- 

 tainly was. The evidence in this case is unfa- 

 vorable to our theory — not quite decisively so, 

 but strongly. For we should expect that in the 

 year of actual minimum disturbance the corona 

 would be even narrower than in this year 1878, 

 which is the year following that of least disturb- 

 ance. And, again, a strongly distinctive feature 

 in the corona of last July was the absence of 

 wide expansions, such as were seen in 1870 and 

 1871. Row, if this peculiarity should really be 

 attributed to the relation existing between the 

 corona and the sun-spots, we should infer that 

 in 1766 the corona would have been still more 

 markedly uniform in shape. The existence of 

 four well-marked expansions on that occasion 

 forces us to assume that either the relation re- 

 ferred to has no real existence, or else that the 

 corona may change at comparatively short inter- 

 vals as the condition of the sun's surface changes, 

 and that in February, 1766, the sun was tempo- 

 rarily disturbed, though the year, as a whole, was 

 one of minimum disturbance. But as the epoch 

 of actual minimum was the middle of 1766, Feb- 

 ruary, 1766, should have been a time of very 

 slight disturbance. I do not know of any obser- 

 vations of the sun recorded for the month of 

 February, 1766. On the whole, the eclipse of 

 1766 must be regarded as throwing grave doubt 

 on the relation assumed by our theory to exist 

 between the corona and the sun-spots ; and as 

 tending to suggest that some wider law is in 

 question than the one we have been considering 

 — if any association really exists. 



The account given by Don Antonio d'Ulloa 

 of the appearance presented by the corona during 



