246 TRANSACTIONS OF THE [mAY 17, 



and American parties, but, I think, added rery little real informa- 

 tion. Professor Hastings made an observation which he believed 

 to establish a peculiar theory proposed by himself, viz., that the 

 corona is merely a diffraction effect ]n-oduced by the moon's 

 limb, and depending on the non-continuity of phase in long 

 stretches of liglit-vibrations. With a peculiar apparatus pre- 

 pared expressly for the purpose, he found that at any moment 

 the 1474 line was visible to a much greater distance from the 

 sun, on the side least deeply covered by the moon, than on the 

 other: as un(|uestionably would happen if his theory were correct. 

 But the same thing would result from the mere diffusion of 

 light by the air; and, notwithstanding his protests, the French 

 observers who were at the same place, and nearly all others who 

 have discussed the observations, think that this was the true ex- 

 planation of wliat he saw. So far as I know, the discussion of 

 the subject which has resulted from his publication has only 

 strengthened the older view — that the corona is a true solar 

 appendage; an intensely luminous but excessively attenuated 

 cloud of mingled gas and fog and dust surrounding the sun, 

 formed and sliaped by solar forces. 



The diffraction theory has one advantage — that it relieves 

 us from stretching our conceptions as to the possible attenuation 

 of matter to the extent necessary in order to account for the fact 

 that a comet, itself mostly a mere airy nothing, experiences no 

 perceptible retardation in passing through the coronal regions. 

 There can be no question that this has hajipened several times: 

 the last instance having been the great comet of 1882. But on 

 careful consideration it will be found, I think, that our concep- 

 tions will bear the stretching without involving the least absurd- 

 ity; a single molecule to the cubic foot would answer every 

 necessary condition of the luminous phenomenon observed. And 

 all the rifts and streamers, and all the radiating structure and 

 curved details of form, cry out against the diffraction hypothesis. 



The observations of the eclipse of 1885 (observed only by a few 

 amateurs in New Zealand) have not proved important. 



At present tlie most interesting debate upon tiie subject 

 centres around the attempt of Mr. Huggins (first in 1883) to ob- 

 tain photographs of the corona in full sunliglit. He succeeded 

 in getting a number of plates showing around the sun certain 

 faint and elusive halo forms which certainly look very coronal. 

 Plans were made and have been carried out, for using a similar 

 apparatus on the Eiffelberg, in Switzerland, and at the Cape of 

 Good Hope. But so far nothing lias been obtained much in 

 advance of Mr. Huggins' own first results. Since September, 

 1883, until very recently, the air has been full, as every one 

 knows, of a fine haze, probably dust and vapor from Krakatoa, 



