654 
Astronomical Notes. 
[November, 
take 42. I said in 1875 B is in 305° with error in more, say 
308° ; its distance is 76, not 300 as Prof. Forbes has it : 
there would have been a conjunction with Uranus between 
1824 and 1829, ^ being at the time in opposition. When 
you examine the “ residuals ” in your article you will find 
this conjunction well indicated, principally when you adopt 
the names I got for A and B in my development theory in 
1857- 
In the papers Le Verrier read before the French Academy 
in 1846 (“ Connaissance du Temps,” 1849, p. 240) he said— ■ 
“ Erreur presque toujours la meme entre 1824 et 27.” 
“ Valeur la plus precise 36*154 ne peut varier qu’entre les 
limites 35*04 et 37*90.” “ 207 a 233 annees envirez.” 
In 1857 I got for Neptune mass 1-14446, pretty near that 
made out by the two I have ; and I believe I can show why 
the figures since obtained by Prof. Newcomb — the one by 
Uranus, the other by a satellite— are more at fault. 
From a Letter to Prof. George Forbes. 
Is the grouping of comets always determined by one planet 
only ? Are the distances of the two planets inferred from 
the mean distances of the groupings the true ones ? Does 
not your cometary method give too free play to the hypo- 
thesis because the number of periods elapsed since the 
catastrophe is selective ? On the other hand, is it not too 
great a restriction to require such close coincidence in longi- 
tude, and to require that the determining planet should 
always have been the one having its orbit next to the present 
aphelion of the comet ? Might it not have been the one 
which was next to that aphelion position at the time of the 
catastrophe, when the planet with the nearest orbit was far 
away ? 
Some comets may have been born within our system ; 
others may enter and leave it ; still others may continue in 
it, and may get condensed, or divided and absorbed. 
The incorporation of the comet is the result of the reduc- 
tion by additional planetary attraction of an original surplus 
of helio-centrifugality, which carried the comet from another 
system into ours, and would carry it out again without this 
disturbance. 
We may consider some aphelia of the Jupiter group as 
originally produced by the inner planets and determined by 
Jupiter, but all crowded round the greatest of planets. 
Between Saturn and Uranus there is no whole group of 
cometary aphelia, but probably a cluster of smallest planetoids 
