SCIENTIFIC SUMMARY. 
267 
the motion of the Moon by taking 1 means to eliminate all the systematic 
errors which have hitherto rendered discordant the results obtained by this 
method. The method of determining the solar parallax by means of the 
parallactic inequality would be, perhaps, the most favourable of all were it 
found possible to eliminate these systematic errors. This Messrs. Campbell 
and Neison have undertaken to do. The value they obtain for the solar 
parallax is 
7T = 8"-778 ± 0"*007 
This value is conditional, however, on the assumption that there is a 
periodical variation in the motion of the Moon due to the action of the 
planets, which systematically affect the value found for the parallactic 
inequality. The fuller inquiry whether there really exist such periodical 
variations, the authors defer to a subsequent research. If there do not 
exist such variations, then they show that the parallax of the Sun is 
7T = 8"- 848 ± 0"-00 7 
Transit of Venus on December 6, 1882. — The Astronomer Royal has 
lately communicated to the Royal Astronomical Society an account of his 
proposed plans for observing the transit of Venus on December 6, 1882. 
The method to be used is Delisle’s, which consists in observing the exact 
time of the ingress or egress of the planet from points on the surface of the 
earth where this ingress or egress is much retarded or accelerated. 
For places where the ingress of the planet on the Sun will be much ac- 
celerated, it is proposed to use stations in the Cape Colony, from the obser- 
vatory at Cape Town to D’Urban. 
For stations where the ingress of the planet on the Sun will be much re- 
tarded, it is proposed to utilize places in the West Indian Islands, and espe- 
cially Barbadoes, Trinidad, and Jamaica. 
For places where the egress of the planet from the Sun will be much 
accelerated, it is proposed to use the same stations as those for retarded 
ingress. 
For stations where the egress of the planet from the Sun will be much 
retarded, it is proposed to use places on the eastern coast of Australia, in- 
cluding Melbourne and Sydney, and, if possible, New Zealand. 
It is proposed to entirely give up the use of photography, on which so 
much reliance was placed by Sir G. Airy and his advisers prior to 1874, 
but which the results of that transit showed to be useless when employed in 
the manner it was. 
It may be remarked that the commencement of the transit will be visible 
in England, commencing shortly before sunset. 
Ultra- Neptunian Planets . — For many years astronomers have speculated 
on the probability of there being several planets belonging to the solar 
system and revolving in orbits beyond that of Neptune. Such a planet 
would probably be so faint and would move so slowly that it might easily 
escape detection for many years. There is, moreover, a peculiar relation- 
ship between the aphelion distances of a number of periodical comets and 
the mean distance of the planet Jupiter , which has led astronomers to 
suppose that these comets have been introduced into the solar system by the 
attraction of that giant planet. There are other comets whose aphelion 
