312 LI, Boss—Tail of Comet b, 1881. 
much greater than 0-6, extremely im robable for that eae 
unless we suppose a high velocity of emission from 
Reus mainly on the side nearest the sun. The Setialons seen 
near the end of this branch of the tail must ae left the nu- 
of the 1807 comet (Oct. Ae pose a value for (L—y) of about 
0°6. (Mose. Ann., vol. v, pt. 2, pine 6). Wema a however oe 
state. Then, on the t Ai of electrical Y cau ie: we shoul 
expect to find a smaller repulsive force for the later date. 
On the whole, the resuJts which can be inferred from table 
ITT in respect to ‘the ratio of the repulsive forces concerned in 
the genesis of the two tails, may be regarded as extremely 
favorable to the hypothesis of Dr. Bredichin, viz: that the tail 
of Type I is due to the presence of hydrogen i in the comet, and 
that of Type IT to carbon. Granting this, we should have ex- 
eae: the traces of hydrogen in the spectrum of the comet to 
have been very pronounced on June 26, or on dates immedi- 
or, at least, a decided change in the character of that portion o 
the spectrum. It must be confessed, however, that all reason- 
ing in the premises must necessarily be vague and unsatisfac- 
tory, since we do not know to what extent matter, in the state 
in which it must exist to form the tail, contributes to the spec- 
trum of those parts of the comet in the vicinity of the nucleus 
and coma, where, alone, spectra have been successfully ob- 
serve 
The ‘complete history of this comet, of the changes observed 
in the nucleus and its surroundings and in the tail, with draw- 
ings, measures and estimated dimensions of all parts will be ex- 
tremely interesting. When collected and combined with results 
of poleraeonis and spectrum analysis, i will doubtless furnish 
most valuable material bearing upon the true theory © the 
constitution of comets. That such material exists in rare abun- 
dance it is not peroniied. us to doubt; and it is to be hoped tuat 
no one who is in possession of definite results, however meager 
in quantity, will hesitate to add them to the collection. 
Dudley Observatory, September 8, 1831, 
