1S66.] Prof. Phillips on a Zone of Spots on the Sun. 69 



tions at short intervals, as twice a day for the whole peniimbral outline, 

 and once an hour for selected critical parts of the umbra. 



EXPLANATION OF PLATE II. 



[The figures are all drawn to represent the objects as tliey appeared in a 6-inch 

 achromatic furnished with the glass mirror set to* reflect the rays in the equatorial 

 plane to the westward. The motion of the spot is from left to right.] 



Fig. 1. Appearance of the spot A, nearly on the central meridian, on Feb. 10th, 1866^ 

 at 11^ 15™, The darkest part of the umbra was to the right; on the left a 

 sharp excvu'i-ent part like a fissure ; between this and the larger and darker 

 part was a lighter brown tract. Small dots on the penumbra in the upper 

 part to the left. Diameter 23,000 miles. 



Fig. 2. First sketch of the spot A after its reappearance, March 5th, lO'' 30™. The 

 long excurrent parts at the extremities of the elliptical figure (elliptical by 

 reason of the proximity of the spot to the edge of the disk) are frequent ap- 

 pearances in this position of the spots. This figure is rather too small in 

 proportion to 4, 5, and 6. 



Fig. 3. Spot A, further on the disk. The figure is rather too small. Note the 

 peculiar shapes of the small fissure-like extensions on the left. March 6th, 

 2^ SO-". 



Fig. 4. Spot A, still further on the disk, March 7th, 10^0™. The ramifications from 

 the umbra have changed in appearance. 



Fig. 5. Spot A, near the central meridian, March 8th, 12^ 30". The two extensions 

 of the penumbra on the left have come into sight smce yesterday. Note the 

 little dot at their com.raon origin, and, directed towards it, the longest of the 

 excurrent umbral fissures. 



Fig. 6. Spot A, March 9th, 12^ 0". Here the excurrent penurabral tracts are found 

 to be separated from the spot, and from each other, and changed in direction , 

 The umbra is much altered, and has a deep emai"gination, in place, appa- 

 rently, of a small white speck, seen in fig. 5. Note also a black speck on the 

 right upper edge of the umbra. 



Fig. 7. Spot C, the largest umbral tract with its border on the right, Feb. 19th, 

 10^ 45'". On account of the remarkable aspect which the umbra wore on 

 this occasion, it was dra-uTi repeatedly with great care. Note in particular 

 the digitations of the large umbi'a, the broad facular space to the right, and 

 the parallel very narrow, interrupted, and tegulated umbral bands, which 

 are part of a system of interrupted small dark tracts, traceable through nearly 

 all the length of the penumbra, Avhich on this occasion was about 100,000 

 miles from end to end. The umbra itself measured about 15,000 miles be- 

 tween the extremities of the digitations. 



Fig. 8. The same parts as they appeared on Feb. 20th, lO'' 20™. The getieral figure 

 of the umbra is changed ; the long parallel narrow black space, and the 

 broader tract on the outside of it are greatly altered ; the latter, turning away 

 from the umbra, appears to have gathered into itself the detached spots which 

 appear in fig. 7, and to have lost the angular tegiilation which then was con- 

 spicuous. 



Fig. 9. In this figure the approacli toward the edge of the sun is sensible in the elon- 

 gation of the large umbra and its companion. Feb. 21st, 2'' 30™. 



Fig. 10 shows the reappearance of this spot C, near the edge, with a divided umbral 

 tract, of different shades of darkness ; the whole figure compressed ellipti- 

 cally by proximity to the edge. March 12th, 12"^ 10"^. 



