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of the long series of observations which have been made under his direction, 
and carefully reduced with the greatest care, and on a uniform principle, 
under his immediate superintendence. The Greenwich Observations afford an 
immense mass of thoroughly reduced observations of the Sun, Moon, planets, 
and stars, such as do not exist anywhere else, and on which will be founded 
in the future, as they have been in the past, the greatest improvements in 
Astronomy. 
Apart from the routine work attaching to his duties, first as Director of 
the Cambridge Observatory and afterwards as Astronomer Royal, and there- 
fore head of the Royal Observatory, Greenwich, the principal astronomical 
labours which have been successfully undertaken by Sir. George Airy are as 
follows: — The determination of the long inequality in the motion of the 
Earth, due to the attraction of the planet Venus, and depending for its impor- 
tance on the fact that every thirteen years Venus and the Earth come back 
to almost the same position with regard to each other. The reduction of the 
Greenwich Planetary Observations from 1750 to 1831, thus placing an im- 
mense mass of observations of the planets, all carefully reduced on a uniform 
system, at the disposal of the theorist who wishes to improve the tables of 
the planets by perfecting the theory of their motion. Since 1751, all the 
observations of the planets made at Greenwich have been carefully reduced 
on the same system, so that at present a long mass of observations are avail- 
able, ranging from 1751 to 1881. Before this was done every mathematical 
astronomer had to reduce the observations for himself, adding most enormous 
amounts of arithmetical drudgery to his other labours. The reduction of 
the Greewich Lunar Observations, from 1751 to 1831, and subsequently the 
extension of this labour up to 1851. This was a still more laborious and im- 
portant labour than the last. It is true that up to the present time it has not 
been employed in the manner that might have been anticipated, as Hansen’s 
Tables were not founded on this great work, being partially constructed be- 
fore it appeared, and no new lunar tables of any importance have since been 
constructed. 
Besides these great works, numerous contributions to the advancement of 
Astronomy are due to Sir G. Airy, such as the publication of Groombridge’s 
Catalogue of Circumpolar Stars ; several expeditions to observe Total 
Eclipses ; the Transit of Venus Expedition of 1874 ; &c. &c. 
Mr. W. H. M. Christie, late the principal Assistant at Greenwich, has 
been appointed the new Astronomer Royal, with Mr. E. Dunkin as his 
principal Assistant. 
BOTANY. 
Reproduction of the Unicellular Algce . — G. Klebs has communicated to 
the Botanische Zeitung (1881, Nos. 18-21) an article on the development of 
numerous unicellular Algae, generally grouped as Protococcaceae. In the 
forms here described, the development is essentially similar; all of them 
are strictly unicellular ; no vegetative division occurs ; each cell lives for 
itself, and at its period of maturity forms a number of daughter-cells, 
