On the Great Comet of 1843. 195 
the two paradoxes already quoted. We hail the favorable opinion 
of this distinguished traveller, who received the Lalande medal 
for the discovery and the elements of the comet of the year 
1821. We are happy further to add the testimony in favor of . 
the plausibility of the period of 21g years, communicated to us 
in writing or verbally by our valued friends, Alexander, of Prince- 
ton; Mitchell, of Nantucket; Gilliss, of Washington; Herrick, 
of New Haven; Loomis, of Western Reserve ; and, nearer home, 
of Professors Patterson and Bache. 
Princeton, Saturday, May 20, 1843. 
My dear Sir—Y our esteemed favor was received last evening. 
I have entire confidence in the scrupulous care with which your 
observations have been conducted, and do not doubt that the com- 
putations founded upon them have been well guarded; yet that 
the comet should have actually struck the sun or his envelope, 
and then rebounded, seems to me to be so violent a supposition, 
as to be inadmissible, except upon compulsory evidence, or in the 
absence of any other rational explanation. Admitting the facts, 
however, to be as above stated, how are we to avoid the conclu- 
sion? I will venture to suggest what Lam at present disposed 
to regard as a plausible solution of the difficulty. 
The centre of gravity of the comet of 1843 was at an unusual 
distance from that which seemed to be the actual nucleus: this 
led to an erroneous estimate of the comet’s position. As, more- 
over, the comet, when first observed, was nearly in its perigee, it 
is altogether possible that the error arising from the cause here 
suggested, was at the same time at its maximum, and that it con- 
tinually decreased until the comet disappeared. ‘The effect upon 
the relative position of the apparent and true orbits would conse- 
quently be such as is roughly represented above—the true or 
dotted orbit deviating more and more from the apparent, as we 
retrace it in the direction opposite to the comet’s motion, and 
thus escaping the sun at the perihelion. 
I am obliged to pause, as the hour has arrived for closing the 
mail. I hope to see you at Philadelphia in a very few days, and 
may perhaps write you again before that time, in answer to the 
question you more particularly propose. 
In extreme haste, yours truly, 
STEPHEN ALEXANDER, 
Sears C. Watxer, Esq., Philadelphia, Pa. 
