282 Prof. E. C. Pickering's Observations of 



ization is produced only by specular and not by diffuse re- 

 flection. 



The spectrum of the corona was observed in the following 

 manner. A common chemical spectroscope was used ; but in- 

 stead of attaching it to a telescope, it was merely pointed in the 

 proper direction a short time before totality. As its field of 

 view was 7 or 8 degrees in diameter, the sun remained in it for 

 a considerable time, and the spectrum obtained was that due to 

 the corona, protuberances, and sky near the sun. On looking 

 through the instrument during totality, a continuous spectrum 

 was seen free from dark lines, but containing two or three bright 

 ones — one near E, and a second near C. At the time, I supposed 

 that these were due to the protuberances ; but Professor Young, 

 with a large spectroscope of five prisms, found a line near E 

 which remained visible even when the image of the protuberance 

 was moved off the slit, and therefore inferred that it was due 

 to the corona. He also found the continuous spectrum free 

 from dark lines — and that one, perhaps three of the bright 

 lines coincide with those of the aurora borealis. These results 

 would lead to the belief that the corona is self-luminous, the 

 bright lines rendering its gaseous nature probable. If it is a 

 part of the sun, even the remoter portions are one hundred times 

 as near as the earth, and would receive ten thousand times as 

 much heat, which would be sufficient to raise any known sub- 

 stance to incandescence. 



Other observations, however, point to quite a different con- 

 clusion. A thermometer with blackened bulb was exposed to 

 the sun's rays and the temperature recorded every five minutes. 

 I found that it began to rise some time before contact, descend- 

 ing again as soon as the moon's limb became visible. It did 

 not reach its former temperature until about a quarter of an hour 

 after the eclipse began, or until a seventh of the sun's disk was 

 obscured. The approach of the moon, therefore, appeared to 

 cause an increase in the sun's heat. The amount of the change 

 was only about 1 0, 3 C, the total difference between this ther- 

 mometer and one in the shade being about 18° C, or in the 

 ratio of 1 to 14. This fraction is but one-half of that given 

 above, owing perhaps to the diminution of heat on the borders of 

 the sun. During totality the difference between the two ther- 

 mometers was almost nothing. In examining the photographs 

 taken by the party, it was noticed that, while the light dimi- 

 nished near the edge of the sun, the moon's limb was very di- 

 stinct, and that there was a marked increase in the light of the 

 parts nearest it. It was suggested that this might be a subjec- 

 tive effect ; but an examination of the photographs is sufficient to 

 convince any one that the appearance is a real one. The glass 



