ents before 1835. If they were
known accurately for 1759, we should no doubt find, that the angle
between the node and perihelion _diminished_ in the interval between
1750 and 1835, as according to the calculations of M. Rosenberg, the
comet was six days behind its time--a fact fatal to the common ideas of
a resisting medium; but this amount of error must be received as only
approximate.

No comet that has revisited the sun, has given astronomers more trouble
than the great comet of 1843. Various orbits have been tried,
elliptical, parabolic and hyperbolic; yet none will accord with all the
observations. The day before this comet was seen in Europe and the
United States, it was seen close to the body of the sun at Conception,
in South America; yet this observation, combined with those following,
would give an orbital velocity due to a very moderate mean distance.
Subsequent observations best accorded with a hyperbolic orbit; and it
was in view of this anomaly, that the late Sears C. Walker considered
that the comet came into collision with the sun in an elliptical orbit,
and its _debris_ passed off again in a hyperbola. That a concussion
would not add to its velocity is certain, and the departure in a
hyperbolic orbit would be contrary to the law of gravitation. This
principle is thus stated by Newton:--"In parabola velocitas ubiquo
equalis est velocitati corporis revolventis in circulo ad dimidiam
distantiam; in ellipsi minor est in hyperbola major." (Vid. Prin. Lib.
1. Prop. 6 Cor. 7.)

But as regards the _fact_, it is probable that Mr. Walker's views are
correct, so far as the change from an ellipse to an hyperbola is
considered. The Conception observation cannot be summarily set aside,
and Professor Peirce acknowledges, that "If it was made with anything of
the accuracy which might be expected from Captain Ray, it exhibits a
decided anomaly in the nature of the forces to which the comet was
subjected during its perihelion passage." The comet came up to the sun
almost in a straight line against the full force of the radial stream;
its velocity must therefore necessarily have been diminished. After its
perihelion, its path was directly _from_ the sun, and an undue velocity
would be kept up by the auxiliary force impressed upon it by the same
radial stream; and hence, the later observations give orbits much larger
than the early ones, and there can be no chance of identifying this
comet with any of its former appeara