Oin the Great Comet of 1843. 189 
of short period of only 21% years; and that it is identical with 
those of February, 1668, and of December, 1689. An early sug- 
gestion of its identity with that of 1668, was made, we believe, 
by Prof. Peirce, in a lecture delivered at Boston, on the 23d of 
March last. Shortly before that date, viz. March 20, it appears 
to have been noticed by Mr. Cooper of Nice, in a letter to 
Schumacher, published in the London Times. 'The question of 
their identity has been discussed by Prof. Schumacher and Mr. 
Petersen of Altona. The latter applies Galle’s elements to the 
perihelion passage in 1668, and Prof. Schumacher expresses an 
opinion in favor of their identity. The subject has been more 
fully discussed by Mr. Henderson, the Astronomer Royal of Scot- 
land; who, in a letter to Schumacher of April L1th, states that 
“there appears great probability in favor of the supposition that the 
late comet, and the one which appeared in 1668 are the same.” 
Mr. Henderson then gives the elements of the comet of 1668, 
and a comparison of the ephemeris computed from them with 
the places of the nucleus of the comet as found by Mr. H. ona 
map in his possession containing a trace of its path among the 
stars, from March 9th to March 21st, 1668, as seen at Goa. The 
agreement is quite sufficient to watrant a conclusion of their 
identity. The first suggestion of the identity of the comets of 
1689 and 1843, was made by ourselves in a letter to the editor 
of the Philadelphia Gazette, April 6th, in which after giving our 
own elements of this comet, and Pingré’s elements of that of 
1689, we mentioned “‘ these elements agree quite well with Prof. 
Peirce’s and ours, except the inclination. 'The observations used 
by Pingré are pronounced to be good by Olbers, and he expresses 
confidence in the elements of Pingré. Still the imperfections of 
instruments and catalogues of stars in 1689, may have caused 
such imperfections of the observations as to lead Pingré to an incli- 
nation of 69°, instead of 39° or 36° as found at present. When 
we consider that the inclination found by Prof. Peirce and our- 
selves is derived from an orbital motion of less than 2°, it is mani- 
fest that the position of the plane of the orbit, or in other words 
the inclination, must be quite uncertain. The same difficulty 
must have occurred in 1689, under still more unfavorable cir- 
cumstances. It is quite likely therefore that a modification of 
the elements of this comet not greater than those of Halley’s 
comet in its successive periods, would represent the observations 
