Remarks on the Tails of Halley’s Comet. 327 
observation of M. de la Nux in 1759, when its maximum lengths 
were 19°, 25°, and 47°. Whenever it presented such lengths, it 
was very narrow, (elle s’ amincissait beaucoup :’”-—and “ l’amin- 
cissement était devenu extréme.”)* It is an interesting coincidence, 
that an unusual narrowness through the greater part of its extent, 
characterized it at its recent appearance when at its greatest lengths, 
i. ey 25°, 35°, and 45°. From this circumstance we may, in the 
absence of any positive information, presume that M. de la Nux 
saw it indirectly. Before the perihelion passage a tail was scarcely 
if at all detected.+ The mean of the above lengths observed on the 
16th, 17th, and 11th of October, 1835, appears to be greater than 
that given by any three observations since 1456, either before or 
after the perihelion passage. This is not to affirm, that, including 
all its dimensions, its magnitude is greater; for, except in 1759, the 
narrow portion may have been wanting. It is, moreover, not im- 
probable, that most observers have given the length as seen with a 
moderate obliquity of the optic axis, a length intermediate between 
the real minimum and maximum for any one instant, or in other 
words, intermediate between the length of the whole and that of the 
part possessing nearly a maximum intensity. 
The greatest length alluded to in the Annuaire as seen at Paris at 
the late return, is 20°. It was with the naked eye, but whether 
with the axis dirsaan toward the object, is not stated. The sky here 
was cloudy and foggy ; length less than 2°. At the observatory of 
Paris on that evening, it appeared but half as long with the finder 
as to the naked eye. This M. Arago pronounces “a result truly 
singular.” I frequently observed the same thing with the five feet 
telescope and attributed it to the moderate aperture of the instru- 
ment. Could not this have been the cause in both cases? This 
effect was not produced by our 24 ft. telescope having a larger aper- 
ture compared with its magnifying power, and was more remarkable 
with the higher than with the lower magnifying powers of the large 
telescope. 
Although the Annuaire contains numerous observations Es the 
length of the tail at the former returns of the comet, it gives but 
three for 1835. The last was by M. Schwabe at Dessau, who found 
it to be 7° on October 26th, when clouds here obstructed the view. 
The new moon and the opacity of * Indian summer” were for a while 
* Annuaire, p. 227. tp. 229. 
