SOLAR EOLirSE, MAY (I, 1883. 121 



We arc forbidden to assitmo that this niidiftnsed A is reflected by particles too large to pro- 

 duce polarization, for the coronal si)ectriun wonld, in every case, exhibit the Fraunhofer lines, and 

 in all but two cases be practically indistinguishable lioni a solar spectrum of the same brightness. 

 The only supposition left is the wholly improbable one that the relative proportion of incandescent 

 matter increases in a very rapid ratio witli increasing distance from the sun. 



The final assumption {d) that the coronal streamers are formed by matter repelled from the 

 sun IS objectionable on account of what it implies. Since the rifts are often many times darker 

 than the streamers, it follows that nearly all the Avhite light comes from such ejected matter. 

 Moreover, since the material docs not give the solar spectrnm, it is not bright because illuminated 

 by the sun, but is selfluminons. We have already alluded to tlie extraqrdinary arrangement of 

 the streamers, as though confined to a plane at right angles to the line of vision. 



PROPOSED EXPLANATION. 



Such objections as have just been considered led the writer, after the eclipse of 1S7S, to seek 

 for a hypothesis free from the obvious defects of the old one. That Ihe origin might possibly be 

 found in the phenomenon of diffraction was an idea early suggested, though it is not at first appa- 

 rent that such an explanation could eliminate the difficulties connected with the polarization of the 

 corona. On flie other hand, the most elementary considerations of the theory of diffraction show 

 that in the case of a total eclipse we should see a ring of light around the moon, brightest on the 

 inner side and extending indefinitely outwards; moreover, that the light of this ring would be de- 

 rived exclusively from areas very near the limb of the sun. That there would be no maxima and 

 minima of brightness in such a ring, either in place or time, follows from the well known fact that 

 within the geometrical shadow such periodic variations are absent. Notwithstanding these fea- 

 tures, so strongly suggestive of the true corona, a quantitative application of the theory of diffrac- 

 tion would seem to render the hypothesis untenable. We may test the validity of the hypothesis 

 thus: 



O .=- ^ , u4 



Let OA be the line of intersection of a plane, passing a point j; on the surface of the earth 

 within the geometrical shadow of the moon and the center of the sun, with a wave surface having 

 its origin in the sun. Also let OB be the intersection, by the same plane, with a spherical surface 

 having its center at jj and tangent to OA at O, with a radius equal to the moon's distance. It is 

 required to find an expression for the illumination at jj due to any point on that solar diameter de- 

 fined by the plane OA jj. This is the well known problem solved by Feesnel. Obviously, for the 

 purpose of investigating the distribution merely, we may consider OA a right line. We will define 

 the position of a point x on this line by its distance from O. 



The velocity of motion produced in a particle of luminiferous ether at j) by an element dx of 

 the wave surface at O is, with proper choice of the origin of time, proportional to 



t 



dx sin 2 ;r p, 



S. Mis. 110 10 



