1866.] Prof. Phillips on a Zone of Spots on the Sun. 65 



The great spot, or rather aggregation of spots, marked C, was observed 

 from the 13th to the 24th of Febraary, as often as good opportunities 

 occurred in the extremely variable weather. When fully expanded, about 

 the 17th, 18th, and 19th of February, it measured about 12° on the surface 

 of the sun, and occupied a space about 100,000 miles long, lying not 

 quite parallel to his equator, and including forty or more black, dark, and 

 dusky umbral tracts, in a complicated penumbral area. The definition 

 was often excellent, so as to show the granular surface of the photosphere 

 with m.ore than ordinary distinctness. 



The same fine brown tint already referred to was observed in the pe- 

 numbral spaces, and there was every gradation of depth in this tint 

 observable in the many specks and spots, till in a few only it seemed to be 

 black. The penumbral tracts were plainly broken up into a kind of net- 

 work of granulation ; and the largest spot, chosen for special study, threw 

 out long black digitations into the surrounding granulated space of the 

 penumbra, like shts in a solid substance, 1000 or 2000 miles in length. 



These characters of the largest spot in the group C became very pro- 

 minent on the 19th of February, and were accompanied by otliers of an 

 unusual character, which seem to deserve special attention in the question 

 of the nature and history of these black spaces. In the drawing for this 

 date these appearances are sketched with a power of 135. The spot was 

 somewhat rhomboidal, the extreme length from angle to angle being about 

 15,000 miles, the least breadth about 4500. On the right the boundary 

 was gently convex ; parallel to it was a bright facular tract of uniform 

 breadth ; this was margined on the right by a nearly continuous very 

 narrow black band, 17,500 miles long, extending in both directions be- 

 yond the spot, and slightly ramose in the (apparently) upper part. Pa- 

 rallel to this again was a curiously interrupted series of black angularly 

 bent sharp cuts, ending upwards in a larger subdigitated mass, near which 

 were some other small spots, forming broken chains, which turned off in 

 curves to the right for about 40,000 miles (PI. II. fig. 7). 



On the 20th of February the appearances had changed to those repre- 

 sented in another sketch (PI. II. fig. 8), where the great spot, something 

 reduced in magnitude and altered in figure, shows very long digitations 

 on all sides ; the facular space on the right is broader ; the long very 

 narrow black band shows two internal extensions ; the outer crested ridge 

 has gathered itself into a shorter figure, 10,000 miles long, and has lost 

 the character of angular tegulation which was so remarkable on the 19th. 



On the 21st the spot had approached enough toward the limb to un- 

 dergo some apparent change of general figure, by contraction perpendicular 

 to the edge ; the facular space on the right was entirely free from the 

 narrow curved black divisional band ; and the summit of the outer broader 

 band was bent away from the great spot, to which it had been parallel 

 (PI. II. fig. 9). The disappearance of the spot amidst large elevated 

 bright faculee and depressed broader shaded tracts, was sketched on the 



VOL. XV. G 



