10 
depths of space with a longer train than any known comet since 
Newton’s day, this chief of comets, in 1843, opened a new epoch of 
activity among all the observatories ; while Plantamour was the 
first of the computers to announce that in its perihelian passage this 
comet must have almost grazed the very surface of the sun. That 
it must have seen for two hours the sun’s incandescent disc under 
an angle of practically 180°, and have been exposed for that length 
of time to a radiation sufficient to vapourise iron, platinum, and every 
known metal ; yet had it lived, preserved its movement, and gone 
off at last apparently uninfluenced on its regular orbit. And what 
kind of orbit was that 1 
Ah ! That indeed is the question ; never more abundantly dis- 
cussed too than at this moment in connection with a comet of the 
present year. Plantamour had been strong enough in his first 
theoretical university essay on the beauty of determining a comet’s 
orbit from three observations ; but he soon learned in practice that 
no three observations ever taken by man, much less the first three 
that are usually secured of such a sudden and unexpected intruder 
as the great comet of 1843, can give more than a very wide approxi- 
mation to that one of all the orbital elements which the public most 
cares for, viz., its period ; and thence the date when it will next be 
seen, as well as that when it was last visible. He showed indeed 
without controversy, that it was a closed orbit, and of no very great 
duration; but whether of 165 years, or 22, or even less — and 
why, in that case it had not been seen oftener, subsequent to its 
supposed record in 1868, he left for the future to determine. 
And now comets followed one another quickly ; the next with 
which Plantamour occupied himself being the second of 1844, 
called the Comet of Mauvais ; and a most opposite one it was to 
that of 1843 in almost every particular. For this of 1844, though 
little more at any time than barely visible to the naked eye, 
remained within telescopic range for nearly nine months ; was well 
and numerously observed during the whole of the time, and gave 
to M. Plantamour’s calculations, perfected as they were in this in- 
stance by his careful introduction of corrections for planetary pertur- 
bations, a perihelion distance of so much as 78 millions of miles; 
and a period, reaching the hitherto unheard of extent, of 102,000 
years, subject to an uncertainty of not more than ^th of the -whole. 
