1900-1901.] Prof. Forbes on. the Ultra- Neptunian Planet. 373 
large that in all probability the new planet has a greater mass' 
than Jupiter. If the new planet be several times the mass of 
Jupiter, the orbit of the comet of 1556 might be so much 
disturbed as to render the comet on its return unrecognisable, if 
the existence of the new planet be ignored. 
A, careful examination of all the comets in Galle’s Catalogue, to 
which elliptic orbits have been assigned has convinced me that 
no one of them is the lost comet 1556. 
At the same time, if the new planet had deflected the comet so 
far as to prevent its return up to now, the planet must have a 
mass so great that its influence on planetary orbits would ere now 
probably have been detected. It is therefore desirable to search 
among the comets to which elliptic orbits have not yet been 
assigned, to see whether any one of them may be the lost comet 
1556. 
Upon making this search, I found that Comet 1844 iii., which 
has been assumed to have a parabolic orbit, would, if its orbit were 
elliptic, have its aphelion in longitude 116°, while Comet 1843 ii. 
would have its aphelion in longitude 115°, and no other comet in 
the whole of Galle’s Catalogue can possibly be identified with 
Comet 1556. It is to the first of these, 1844 iii., that I wish in 
the first place to draw attention. According to the ephemeris 
published by me, the aphelion longitude of this comet was 
occupied by the planet in the year 1705, i.e., about the same time 
as the comet itself. Both Encke and Cooper ( Cometic Orbits , 
p. 173), besides others, have noticed a similarity between this 
comet and 1556. I find that if this comet be moving in the 
disturbed orbit of 1556 the Node has been retrograded consider- 
ably, the inclination has been increased, and the longitude of 
Perihelion has been advanced. In all these points it agrees with 
the character of the perturbations that we should expect the new 
planet to produce, as stated above. Also the line of intersection 
of the two orbits is near their aphelia, and is approximately in 
the position suggested by a preliminary examination. Only the 
latitude of Aphelion is smaller than would be expected on any 
moderate assumption as to the mass of the planet. This is the 
only apparent discrepancy that appears in the preliminary investi- 
gation. In all other particulars the orbit of Comet 1844 iii. 
