194 On the Great Comet of 1843. 
and which we alluded to in our published letter of April 6th, 
namely, the error arising from measuring the place of the densest 
point of the nucleus instead of the common centre of gravity of 
the nucleus and tail. We give below his letter in full. We have 
also had placed in our hands by Professor A. D. Bache, a letter 
from Professor Bartlett, of West Point, dated May 23d. We give 
below that part of his letter which treats on this subject, remark- 
ing that we have no doubt that the coincidence in opinions of 
Mr. Herrick, Professor Alexander, and Professor Bartlett, has ta- 
ken place without either one having any knowledge that the same 
idea had occurred to the other two. We would also remark that 
the criticism of Professor Bartlett, on Arago’s parabolic elements 
and on our own, is just, and confirms our statements that no para- 
bolic ephemeris will perfectly represent consecutive observations 
of this comet. We know of only two sets of elements that will 
give a good ephemeris; the one is Encke’s and the other is ours. 
Both are hyperbolic and paradoxical. We give them below. 
The explanation of Professors Alexander and Bartlett, we have 
no doubt, isthe true one. It is plain and natural, and @ prior: ex~- 
tremely probable. It will also satisfy the criticism of Professor 
Anderson, in as much as it points out the particular source of the 
error of the data, which Dr. Anderson supposed must exist some- 
where. ‘The explanation is doubly satisfactory for ourselves, 
since it leaves the way clear for the establishment of the short 
period, and the identity of the three comets of 1668, 1689, and 
1843, and leaves us still a hope of seeing this remarkable vis- 
itor in 1865. Moreover it does away with both paradoxes, and. 
shows at the same time, that the European astronomers, as well 
as ourselves, who were led into them, arrived at them in the le- 
gitimate and only possible mode of observation and computation. 
Professor Bessel, of Kénigsberg, the greatest living astronomer, 
and since Olbers’s death, the most experienced and sagacious ob- 
server of comets, remarks in a letter to Prof. Schumacher, dated 
March 28th :—‘‘ This comet seems to have expended the greater 
part of its nucleus in building up its splendid tail.” 
We are happy to add the testimony of our friend Mr. Nicollet 
in favor of the strength of these analogies, and of the probable 
return of this comet in 1865, as an inference not to be in the 
slightest degree shaken by the fact that a nice discussion of the 
observations of the apparent centre of the nebulosity has led to 
