SOLAll ECJLirSE, MAY 0, 18So. 119 



sitiou of a ooroiial iitmosphei'e. First, the pliotographs indicate wliat may be styled a flat 

 arrangement of the corona, as though the forces whicli produce its irregularities act only in a 

 l)laue at right angles to the line of vision. That is to say, the rifts and streamers seem to have 

 their origin at or uear the limb of the sun and are often narrowly limited in width. Such a char- 

 acter might well exist if the corona were determined by the disk of the sun, but would be highly 

 improbable if it were distributed about the solar globe; secondly, we are compelled by this theoj-y 

 to assume most improbable changes in the hypothetical atmosphere. For example, the line 1474 

 K was traced to a distance of 1,200,000 miles from the sun in 1874, while four years later it was 

 so feeble as to have eluded all but two of the observers, notwithstanding that the conditions of 

 vision were probably better then than ever before. If the line demonstrates the existence of an 

 atmosphere, it demonstrates also inconceivable changes in it. 



In regard to the matter (6) which emits the white light, our statements must be a little less 

 positive. That it is not of solid or liquid particles suspended in an atmosphere after the nature 

 of our clouds is pretty evident from the necessary rarity of such an atmosi)here.* The sui)position 

 tlmt a large quantity of meteoric matter is falling into the sun otters almost as great difficulties. 

 We must conclude that it is falling nearly vertically downwards in the immediate neighborhood 

 of the sun, because the necessary orbital velocities to check this precipitation could not exist 

 within an atmosphere, eveu if we disregard the difficulties in the way of accepting a theory which 

 implies a swarm of satellites whose orbital poles are distributed uniformly over the heavens; 

 hence there must be a continuous supply from without. This supply cannot come from parabolic 

 comets unless those of small perihelion distances are more abundant thau those of great. I am 

 uot aware that there is any evidence, founded either on theory or observation, which cannot be ex- 

 plained by the greater brightness of comets near the sun, and hence their greater liability to dis- 

 covery, for such a distribution of perihelion distances. It is true that such a law for periodic 

 comets might be probable, but as these are likely to have the poles of their orbits uear the poles 

 of the ecliptic, they, although they serve admirably to explain the zodiacal light, could not give 

 such a corona as we observe. Perhaps the assumption of an inter[)lanetary resisting medium 

 would help the hypothesis of a nieteoric constitution, but it would be another hypothesis. The 

 possibility of matter ejected from the suu we will consider with the structure of the corona. 



The polarization (c), when considered quantitatively, is even more incompatible witii the 

 accepted theory than either of the phenomena previously discussed. It is clear, as has been pointed 

 out by a number of writers, that the polarization of light retlected from a i^article at the surface 

 of the suu is nil, because the luminous source there is a surface with an angular subtense of 180°. 

 It is also easy to see that therefore the polarization of the corona near the limb of the moon must 

 be small, eveu if all the light is diffused by matter in such a state of subdivision as to give a maxi- 

 mum effect. At a greater distance from the moon the percentage of polarization should be greater. 

 But this is quite contrary to the observed law. In 1878 I mnde a number of approximate calcula- 

 tions as to the percentages of polarization at various distances from the moon, and found them 

 widely at variance with the estimated values in my own observations. In December, 1879, Dr. 

 Schustert published an elaborate analytical discussion of the problem. We will make use of the 

 results of his investigation. These, under various assumptions as to the law of distribution of 

 matter about the sun which should diffuse light so as to give the maximum amount of polarization, 

 are given in the accompanying table : 



* It is perhaps worth noting that whatever argument can he drawn from the independence of the viscosity of a 

 gas or pressure and its increase with temperature cease to apply when the mean free path is large compared to the 

 dimensions of the hody considered. « 



tR. A. Soc. Month. Not., vol. 40, p. 36. 



