1882.] Photographing the Solar Corona without an Eclipse. 409 



series it is 302*5. Again, the mean sun-spot value for the first series 

 is 328, while for the second series it is 277. A difference in mean 

 spotted area of 51 million ths of the visible disk would therefore 

 appear to correspond to a difference in terrestrial magnetic intensity 

 equal to 15*9 hundred thousandths of the whole. The results of 

 Tables I and II are exhibited graphically in the diagram. 



8. If we refer to this diagram we shall see that the appearance of 

 the curves representing magnetic change is very similar to that of the 

 curves representing solar change, but that the epoch of maximum 

 or minimum for the latter slightly precedes the corresponding epoch 

 for the former. 



The magnetic means recorded by Broun, from which these results 

 have been derived, are for the Gottingen astronomical day (Oh. to 

 23 h.), while the sun-spot observations were made by Schwabe and 

 Dessau, at times not far distant from noon (0 h.). Had the two sets of 

 carves, terrestrial and solar, marched exactly together, we might thus 

 have inferred that in reality the terrestrial (corresponding to 12 

 hours), was behind the solar (corresponding to times not far distant 

 from Oh.). But in addition to this, the curves denote a decided 

 precedence of the solar over the terrestrial. There is thus con- 

 siderable evidence in favour of a lagging behind on the part of the 

 terrestrial results, and hence in this respect these magnetic pheno- 

 mena of very short period form no exception to other magnetic 

 phenomena, such as those connected with daily range, which exhibit a 

 lagging behind the corresponding solar changes in a very un- 

 mistakable manner. 



III. " On a Method of Photographing the Solar Corona without 

 an Eclipse." By William Huggins, D.C.L., LL.D., F.R.S. 

 Received December 13, 1882. 



Problems of the highest interest in the physics of our sun are 

 connected, doubtless, with the varying forms which the coronal light 

 is known to assume, but these would seem to admit of solution only 

 on the condition of its being possible to study the corona continuously, 

 and so to be able to confront its changes with the other variable 

 phenomena which the sun presents. " Unless some means be found," 

 says Professor C. A. Young, " for bringing out the structures round 

 the sun which are hidden by the glare of our atmosphere, the progress 

 of our knowledge must be very slow, for the corona is visible only about 

 eight days in a century, in the aggregate, and then only over narrow 

 stripes on the earth's surface, and but from one to five minutes at a 

 time by any one observer."* 



* " The Sun," p. 239. 



