164 
SECOND REPORT- 1832. 
be the same. It was row found that the later observations 
might be reconciled by supposing a periodic time of 2460 days, 
but the earlier observation required 2469 days. There seems 
no doubt of the identitity of the three comets ; but as the earlier 
perturbations have not been computed, it is doubtful whether 
this difference depends on perturbation or resistance of a me¬ 
dium. In an elaborate paper in the Memoires de VInstitute 
tom. 8, Damoiseau has calculated the perturbations of the mean 
anomaly and axis major from 1808 to 1826, and those of all the 
elements from 1826 to 1832 ; and an ephemeris for the present 
year, grounded on these, is printed in the Supplement to the 
Nautical Almanac. This comet will pass in the present year 
within 20,000 miles of the earth’s orbit. The motions of the 
three new periodical comets (including Olbers’s of 74 years,) are 
in the same direction as those of the planets. The motion of 
Halley’s comet, however, is retrograde. 
Much labour has been employed in calculating the elements 
of Halley’s comet for 1835. In the Ast. Nadir . No. 180, Ro¬ 
se nberger has deduced from observations the elements at the 
last appearance: and in No. 196, the elements at the appear¬ 
ance of 1682. In the results he has given the effects of an 
error in the assumed value of the major axis. In the Turin 
Memoirs 1817, is a most elaborate paper by Damoiseau on the 
perturbations of its elements between 1682 and 1759, and also 
between 1759 and 1835. I am not aware that the whole of 
these (which are undoubtedly the best materials,) have been 
combined to give a prediction for 1835. In the Conn, des 
Temps 1833, Pontecoulant determines the elements for 1835 
by a similar calculation of perturbations applied to the elements 
which Burckhardt had obtained {Conn, des Temps 1819,) for 
1682 and 1759. 
A great number of old comets have been calculated, princi¬ 
pally by Burckhardt and Olbers, but I know of no interesting 
result. In the Memoires de TInstilut 1806, is an elaborate paper 
by Burckhardt on Lexell’s comet of 1770. There seems no 
doubt that, from the perturbations of Jupiter, its parabolic orbit 
was changed into an elliptic orbit of about 5^ years, and that 
this was much altered by the earth’s perturbation: but the 
further history of the comet is unknown. Burckhardt is in¬ 
clined to think that it may possibly still be a periodic comet; 
or possibly a satellite of Jupiter, as it would not at the distance 
of Jupiter be visible to us. 
On the physical constitution of comets we have learnt nothing, 
except that they appear to be wholly gaseous. In the beginning 
of the century there were many discussions in Germany re- 
