1878.] last two total solar eclipses. 215 



corona is drawn out has been variously designated as the sun's 

 equator or as the ecliptic; the two are inclined at an angle 7° only, 

 so that it may be difficult to decide between the two. We may 

 dismiss at once the idea that the greater extension of the corona 

 is due to the centrifugal force caused by the sun's rotation, for the 

 outline is not at ail-that of a surface which could be produced by 

 such a force. We have then only two explanations to account for 

 it. If we look at the corona simply as an atmosphere of the 

 sun disturbed from inside, we might say that the greatest dis- 

 turbances take place near the equator, and that therefore the gases 

 might be thrown up higher there. Those however who look 

 partly outside the sun for the explanation of the corona, would 

 say that those meteor streams which cause the appearance of the 

 corona might circulate in a plane which is but little inclined to 

 the ecliptic, as, for instance, the zodiacal light lies approximately 

 in the direction of the sun's equator. 



There is, I think, much to be said in favour of this latter view, 

 for the difference between the equatorial and polar regions is 

 much more striking in the outer regions of the corona than it is 

 in the inner regions, and these long streamers of light, extending 

 to a distance of 10 solar diameters, which have been observed 

 during the late eclipse on the top of Pike's Peak, can hardly be 

 due to anything proceeding outward from the sun. There is how- 

 ever in addition to this symmetry in the sun's corona a departure 

 from symmetry which occurs pretty regularly. It is that the 

 corona seems longer and wider on one side of the sun than on 

 the other. Thus, for instance, the corona of 1875 resembled that 

 of 1874, not only through the fact that both times it is extended 

 in the direction of the sun's equator, but also that the branch 

 which lies towards the west is wider than that towards the east. 

 In the eclipse of .1868, the opposite apparently held good. The 

 fact that the two eclipses of 1874 and 1875 took place when the 

 sun and earth were approximately in the same relative position, 

 while in 1868 there was an angle of 120° between the longitudes, 

 suggests that the departure from symmetry to which I have 

 alluded depends on something which is fixed in space. 



The connexion which several observers believe to have found 

 between the solar corona and sun-spots has led me to look over 

 the drawings and photographs of former eclipses, and to see 

 whether any difference can be found in the general outline of the 

 corona during periods of maximum or minimum sun-spots. I have 

 been unfortunately restricted to the eclipses of 'the last 10 years, 

 but there can be no doubt that during these 10 years the corona 

 has undergone a gradual transformation, and that it has now come 

 back again to approximately the same shape it had 10 years a^o. 

 In the eclipse of 1868, we find small polar rifts and on each side 

 Vol. III. Pt. v. 16 



