48 Prof. Phillips Physical Aspect of the Sun. [Jan. 26, 



elevated parts should project beyond the general circular outline. This I 

 have never seen to happen ; and if a little attention be given to proportions, 

 it will appear very unlikely to be often observed. If the breadth of one of 

 the ridges be taken at 4000 miles, its average slope 30, and its height at 

 a quarter of the breadth, viz. 1000 miles, this, if projected beyond the 

 circular disk, would no doubt be discernible, for it would be equal to -g^th 

 of the sun's diameter, or above 2". But the number of the ridges is so 

 great, and the crowding of them very near and on the limb go close, that 

 it is hardly possible, on the average, for any ridge to be seen much above 

 its fellows, whether the faculae be in the atmosphere or in [the body of 

 the sun. 



The continuous circularity of the sun's limb is therefore no sufficient 

 argument in itself against the faculao being much raised above the general 

 surface ; and it seems worth while to make special researches as to the 

 manner in which faculae come on and go off, in the hope of finding some 

 case which shall be decisive. 



General Ground. In examining the interspaces between the faculse in 

 the parts towards the limb, it is not easy to see more on the surface thus 

 inclined to the visual ray than a certain unevenness of tint ; under a higher 

 angle of incidence, toward the interior of the disk, this ground acquires 

 more evident partial shades and lights a sort of granulation difficult to 

 analyze, especially if, as is most frequent, the edge of the sun shakes with 

 varying refraction. If all be quite steady, however, the eye discerns both 

 the ramifications of faculae and the granulation of the interspaces, and 

 bv degrees acquires the power of seeing this easily and clearly. Under 

 this condition, the perpetual motion and inconstant agitation, so often 

 described, by no means appears to be a characteristic phenomenon, but 

 rather as an exceptional trouble to the observer, arising from inconstant 

 refraction, fatigue of the eye, or shake of the instrument. These diffi- 

 culties increase rapidly with high powers ; but with a power of 1 00, and 

 good weather, the sun's face does not appear to be much obscured by 

 this kind of intestine agitation. 



What is seen appears in the diagram for April 2, 1864, as well as I 

 can represent a structure so minute and perplexing. The ground of the 

 whole is a surface of complicated small lights and shades, the limits of 

 which appear arched or straight or confused according to the case ; and 

 the indeterminate union of these produces sometimes faint luminous 

 ridges, the intervals filled up by shaded interstices and insulated patches 

 of illuminated surface. One eminent observer *, seeing these under a 

 high power, has compared them to willow leaves, unarranged except where 

 they conform in some degree to the great features, of the spots. Using 

 the same kind of analogy, one might say they seem to resemble any some- 

 what uneven surface composed of separate masses, presenting themselves 

 in all directions and at different levels. Being of all shapes, they must 

 generally have one transverse measure greater than the other, and thus 

 * Mr. Nasmyth. 



