2 ROUGH WAYS MADE SMOOTH. 



corona and the sun-spots be satisfactorily established, an 

 impoffctn-r.step iji ^advance will have been made, possibly 

 even the- 'key .t6/*tlle.\.^higilia will be found to have been 

 di/eoVerqcL*. ...... f 



I'rjfopOsxJ*n6wf to poiisicler, first, whether the evidence 

 we have on this sub'ject 'is* 'sufficient, and afterwards to 

 discuss some of the ideas suggested by the relations which 

 have been recognised as existing between the sun-spots, 

 the sierra, the coloured prominences, and the zodiacal light. 



The evidence from the recent eclipses indicates beyond 

 all possibility of doubt or question, that during the years 

 when sun-spots were numerous, in 1870 and 1871, the 

 corona, at least on the days of the total solar eclipses in 

 those years, presented an appearance entirely different from 

 that of the corona seen on July 29, 1878, when the sun was 

 almost free from spots. This will be more fully indicated 

 further on. At present it is necessary to notice only (i) 

 that whereas in 1870 and 1871 the inner corona extended 

 at least 250,000 miles from the sun, it reached only to a 

 height of some 70,000 miles in 1878 ; (2) in 1870 and 

 1871 it possessed a very complicated structure, whereas in 

 1878 the definite structure could be recognised only in two 

 parts of the inner corona ; (3) in 1871 the corona was pink, 

 whereas in 1878 it was pearly white; (4) the corona was 

 ten times brighter in 1871 than in 1878 ; lastly, in 1871 the 

 light of the corona came in part from glowing gas, where- 

 as in July, 1878, the light came chiefly, if not wholly, from 

 glowing solid or liquid matter. I must here point out, that 

 the evidence of change, however satisfactory in itself, would 

 be quite insufficient to establish the general theory that the 

 corona sympathises with the solar photosphere in the special 

 manner suggested by the recent eclipse observations. 

 There are few practices more unscientific, or more likely to 

 lead to erroneous theorising, than that of basing a general 

 theory on a small number of observations. In this case we 

 have, in fact, but a single observed correspondence, though 

 the observations establishing it form a series. It has been 



