REPORT ON ASTRONOMY. 
169 
world by Captain Hall, Sir Thomas Brisbane, Mr. Goldingham, 
&c. A vast number of most careful observations by Captain 
Foster, in his last voyage, has been received in England, and is 
now (I believe) preparing for the press. Advantage has also 
been taken of our repeated expeditions to the North Seas to 
observe pendulums at high latitudes. The method commonly 
used by the French philosophers was, to observe the absolute 
length of the seconds pendulum at each station: thus they ex¬ 
perimented at several stations in France and Italy, in the Me¬ 
diterranean, and in Britain. An extensive series, however, 
made in Freycinet’s voyage, and a few in Buperrey’s, were made 
with invariable pendulums. In the course of experiments for 
ascertaining the absolute length of the seconds pendulum by a 
new method, Bessel found that the correction applied in all 
former experiments for the buoyancy of the air was defective. 
This has been fully confirmed by Captain Sabine’s experiments 
in a vacuum; and Mr. Baily has been actively employed in de¬ 
termining, with superior accuracy, the correction that ought to 
be adopted. This error, however, produces very little effect 
on the determinations of the proportion of the force of gravity 
at different places. 
A series of pendulum experiments was made by Carlini, at 
the Hospice of Mont Cenis, to ascertain the diminution of gra¬ 
vity at the height of a thousand toises. The account of these 
is given in the Milan Ephemeris for 1824. The result obtained 
for the mean density of the earth agrees pretty well with that 
generally received; but the changes which experiment has 
shown to be necessary in the elements of reduction, throw a 
little doubt upon its value. The mountain Schehallien (on 
which Maskelyne’s observations of attraction were made,) has 
been surveyed, and some alteration made in the numerical re¬ 
sults ; the calculations of Cavendish’s experiments have also 
been corrected. See various volumes of the Phil. Trans. 
In the theory, no improvement has been made, I believe, since 
the time of Clairaut. No satisfactory rule has been given for 
taking into account the elevation of the station: perhaps the 
considerations suggested by Dr. Young in the Phil. Trans. 
1819, may be regarded as the most useful. 
It is generally thought that the measures of arcs give an el- 
lipticity of nearly to the earth ; some persons considering 
it a little greater, and others a little smaller. The pendulum 
experiments, with Clairaut’s theorem, give an ellipticity rather 
greater, though not without remarkable anomalies. 
IX. About the year 1800 the following may be considered 
