240 On the Physical Appearance of the Comets b and ¢, 1881. 
P). XIX., Fig. 3. July 24, 11h. 47m.—about 12h. 20m. Squally. Heavy cirro- 
strata continually passing. Comet visible for short intervals only. 
Nucleus very bright and very well defined, extended towards the apex, certainly 
not towards the sides, looks rather likea fan. ‘‘ Shadow” visible, contrast between 
it and the tail not very strong, no trace of it in the tail a little further from the 
nucleus. Tail very rapidly much fainter. The nucleus projects into the “ shadow” 
as in drawing ; the fan-like appearance very decided. Light from nucleus towards 
coma very suddenly decreasing. The light-fan terminates on the following side 
more abruptly than on the other ; it seems sometimes to consist of different rays. 
Pl. XIX., Fig. 4. July 27, 10h. 30m.—about 1ih. 0m. Moderately clear, then 
overcast. 
The comet is very much like the drawing of July 20, but considerably fainter 
and smaller. Nucleus very well defined. ‘(Shadow ” extremely faint. Coma very 
gradually less bright ; no light-fan, more a general halo. Radius of coma rather 
small. A segment seems sometimes to be cut out of the apex. 
Pl. XIX., Fig. 5. July 31, 9h. 50m.—about 10h. 50m., 11h. 50m.—12h, 20m. 
Very clear. Sky at first very bright. 
Comet considerably fainter. “Shadow” indistinct, but perceptible, nucieus 
projecting into it. Traces of a light-fan on the preceding side, terminating rather 
abruptly on the following one. There seem to be bright streamers in the fan. 
One side-ray towards the following side as in drawing ; coma as if interrupted by a 
darker sector. Light of coma very gradually fainter. Side-ray much fainter than 
the preceding fan. 12h. 0m. All the details rather indistinct, yet certainly 
visible. Tail rapidly less bright, side-ray very faint. “Shadow” hardly defined, 
more like a gradual decrease of brightness as on July 20. 
Pl. XIX., Fig. 6. August 1, 10h. 30m.—10h. 50m. Sky very hazy. 
Nucleus very well defined, very sharp. Not much detail visible. Traces of a 
fan. Traces of the “shadow,” the latter without any sharp outline ; outline of fan 
likewise very indistinct. Radius of coma rather small. A star very well visible 
through the comet, the nucleus decidedly brighter. 
Comet c, 1881. 
Pl. XIX., Figs. 7 and 8. August 19. Clear ; hazy clouds passing. 
9h. 15m. Nucleus well defined, and very bright. From it something like a light- 
fan. Light towards apex (near nucleus) brighter. Tail bright, but considerably 
fainter than the nucleus ; in the tail behind the nucleus a dark line. 
9h. 35m. No structure visible. General fan-like halo. Fan not very sharply 
defined. 
9h. 50m. Nucleus projecting into the “shadow,” which is rather faint. Light on 
both sides of the apex brighter; this sometimes very distinct. The fan hes 
sometimes a little towards the preceding side. The following part of the “ shadow,” 
