1870.] 



as observed in the United States. 



183 



" A faint continuous spectrum, without any traces of dark lines in it, was 

 also visible, evidently due to the corona. Its light, tested by a tourmaline 

 applied next to the eye, proved to be very strongly polarized in a plane 

 passing through the centre of the sun. I am not sure, however, but that 

 this polarization, as suggested by Prof. Pickering, may have been produced 

 by the successive refractions through the prisms. This explanation at once 

 removes the difficulty otherwise arising from the absence of dark lines." 



I have first to do with the continuous spectrum, deduced from Professor 

 Pickering's observations. 



I think in such a method of observation, even if the corona were terres- 

 trial and gave a dark line spectrum, the lines visible with such a dim light 

 would in great part he obliterated by the corresponding bright lines given 

 out by the long arc of chromosphere visible, to say nothing of the promi- 

 nences, in which it would be strange if C, D, E, b, F, and many other lines 

 were not reversed. This suggestion, I think, is strengthened by the state- 

 ment that two bright lines were seen "near C" and "near E;" should 

 we not rather read (for the "near" shows that we are only dealing with 

 approximations) C and F, which is exactly what we might expect. 



But even this is not all that may be hazarded on the subject of the con- 

 tinuous spectrum, which was also seen by Professor Young under dnTerent 

 conditions. 



Assuming the corona to be an atmospheric effect merely, as I have 

 before asserted it to be, it seems to me that its spectrum should be conti- 

 nuous, or nearly so ; for is it not as much due to the light of the promi- 

 nences as to the light of the photosphere, which, it may be said roughly, 

 are complementary to each other? 



"With regard to the aurora theory, I gather from Professor Young's note 

 that, if not already withdrawn, he is anxious to wait till the next eclipse for 

 further facts. I consider that the fact that I often see the line at 1474, 

 and often do not, is fatal to it, as it should be constantly visible on the 

 proposed hypothesis. The observation of iron-vapour, as I hold it to be 

 at this elevation, is of extreme value, coupled with its simple spectrum, 

 seen during an eclipse, as it entirely confirms my observations made at a 

 lower level in the case, not only of iron, but of magnesium. 



