Prof. W. A. Norton on Donati’s Comet. 81 
action. If this be the true explanation of the phenomenon, we 
have in the observed distance between contiguous bright bands, 
the means of determining the period of rotation ; or, at least, the 
shortest interval of time in which the rotation can be completed. 
If we take this distance at 1°, the period of rotation comes out 
about 24 hours, , 
ere was a special cause of lateral dispersion at work in the 
case of the cometary particles that, on their return, came very 
hear the nucleus. Such streams of particles must have been re- 
pelled off obliquely, and may very well have presented the ap- 
ce of luminous jets issuing from the sides of the nucleus, 
and have formed curved terminations to the inner envelope. 
From the dispersion thus produced resulted an a 
ter, or a dark 5 ace, behind the nucleus, whose varying boundary 
Was determine by the intersections of lines of particles unequally 
Tepelled by the sun. . : 3 
The indications are, that the formation and gradual expansion 
. one envelope after another, may have arisen from the process 
of ejection beginning in all instances high up in the photosphere 
Surrounding the nucleus, and gradually extending downward to 
the vicinity of the solid surface. It appears, upon investigation, 
that if this descending action were to proceed according to a cer- 
tain uniform law, the outline of the envelope would recede from 
the nucleus at a uniform rate. This process of evolution of com- 
etary matter, in whatever it may consist, is probably auroral in 
an vtigin and character, and has its counterpart on both the earth 
sun, 
Segre 
New Haven, Noy. 30, 1859. | 
*To render the investigati lete, I have considered the case of the 
vestigation more complete, I ha eG 
- imetary mate i j ym the nucleus, without experiencing any repul- 
— Sion from its a projected from 
ND SERIES, Vol. XXIX, No. 85.—JAN., 1860. 
11 
