(240.) 
Captain 
Kater ; 
his con- 
vertible 
pendulum. 
852 
and Baily. As regards the determination of the 
Earth’s figure, the relative length of a pendulum vi- 
brating seconds in different latitudes is all that is re- 
quired; but the absolute length in a given place is 
necessary for finding the force of gravity there ex- 
pressed by the acceleration of falling bodies in vacuo 
in one second ; and as the British standard yard was 
at that time made to depend on the length of the pen- 
dulum vibrating seconds at London, this enquiry was 
mixed up with the intricate one of National Standard 
Measures. 
Caprain Henry Karer was a person of remarkable 
mechanical skill and ingenuity, and his numerous pa- 
pers in the Philosophical Transactions, between 1813 
and 1828, refer chiefly to the accurate construction 
and use of the Pendulum, the Balance, and certain As- 
tronomical Instruments. He first applied to practical 
use the beautiful theorem of Huygens respecting the 
convertibility of the Centres of Oscillation and Sus- 
pension of the pendulum. A metallic bar pendulum 
was provided with two parallel knife-edges facing op- 
posite ways, and upon either of which it might be 
swung. They were so arranged that when either was 
used as the point of suspension, the other nearly re- 
presented the centre of oscillation, and by means of 
a small adjustable weight, this condition might be ac- 
MATHEMATICAL AND PHYSICAL SCIENCE. ‘ 
[Diss. VI. 
of a perfectly sound and uninterrupted state of health 
until his 70th year. His intellect partook of the 
equable tone of his bodily powers. Method, and an and charac- 
ardour which, instead of acting by impulses, seemed 
inexhaustible and unvaried, were the secrets of his 
success. Mr Baily never was hurried, and he never 
was unemployed. He had always leisure to encourage 
men of like tastes, and he was never unwilling to learn 
from any one who had knowledge to communicate. 
To do one thing at a time was his first principle. 
When thoroughly accomplished, it was completely put 
aside, and a fresh subject undertaken. Whether an 
experiment or a calculation was found to require a 
month or three years, it was pursued to a successful 
completion, without stint or grudging. No amount 
of contrariety and failure in such matters was ever 
known to ruffle his temper, or to make his persever- 
ance falter. 
Francis Baily was known, in the first place, as the 
founder (in 1820) of the Astronomical Society of 
(243.) 
Founded 
the Astro- 
London, an institution of signal utility, which has nomical 
ever since been conducted with great judgment and Society. 
success. His accurate knowledge of past and current 
astronomical history, and his personal acquaintance 
with most European astronomers, enabled him to 
conduct its affairs with great advantage. 
curately fulfilled; in which case (by Huygens’ princi- 
ple) the distance between the knife-~edges corresponded 
accurately to the length of an equivalent simple pen- 
dulum, This elegant application was farther tested 
Amongst his other acquirements, he studied his-  (244.) 
tory and chronology with his customary precision. A ue 
very able paper on the date of the ¢elebrated Eclipse a aa tes - 
of Thales was his earliest scientific publication,’ and Catalogues. 
(241.) 
His Colli- 
mator. 
(242.) 
Francis 
Baily ; 
his early 
history 
by Mr Baily, but it was found liable to serious prac- 
tical objections. Baily dispensed with the sliding 
weight, and rendered the pendulum invariable: the 
distance of the knife-edges was adjusted by grinding. 
To Kater we owe the invention of the floating Col- 
limator, for ascertaining the accurate zero or level 
points of divided astronomical instruments. The op- 
tical principle on which it depends is a very beau- 
tiful one, and the invention of Kater, with several 
improvements in point of form, has become the auxi- 
liary of nearly every observatory in the world. It is 
one of those small but happy improvements which 
affect materially the progress of Science. 
Francis Batty, who was born 28th April1774, and 
who died 30th August 1844, was an instance of a 
person not endowed with extraordinary talents, yet of 
singular use in his generation. Those who knew Mr 
Baily personally, and what he accomplished for Astro- 
nomy, are best aware how rare and yet how estimable 
are such qualifications as his. Born of parents of a 
middle rank of life, educated at a country school, and 
at an early age thrown into the vortex of commer- 
cial life in the city of London, no probability could 
have appeared more remote than that he should ac- 
quire the respect of even the most accomplished As- 
tronomers by his scientific acquirements and perform- 
ances. He enjoyed the advantage, in the first place, 
the literature and phenomena of solar eclipses oceu- 
pied his particular attention ever afterwards. His ac- 
counts of the Eclipse of 1820, of the Annular Eclipse 
of 1836, which he observed at Jedburgh, and the Total 
Eclipse of 1842, with its marvellous revelation of the 
rose-coloured protuberances of the solar atmosphere, 
are among the most interesting and classical of his 
writings. He promoted greatly the formation and 
publication of accurate Star Catalogues, and he in- 
vented, independently of Bessel, constant numbers 
for facilitating the calculation of Precession, Nuta- 
tion, and Aberration, as affecting the places of parti- 
cular stars. He also published a most useful collec- 
tion of Astronomical Tables and Formule, and an 
elaborate and very curious life of Flamsteed. 
I shall now proceed to notice his experiments on 
the Pendulum, which are more particularly connected 
with the present section. 
Mr Baily’s most important observations were on 
a correction of the motion of a pendulum long mis- 
(245.) 
(246.) 
Baily’s 
pendulum 
understood. The corrections usually admitted were observa- 
the following:—1. For tem 
length of the pendulum. 2. For the height of the 
station above the level of the sea. Dr Young showed 
that this correction was commonly overrated, owing 
to the sensible amount of the attraction of the ele- 
vated land on which the experiment is made. 3. For 
1 Phil. Trans. 1811, 
perature altering the tions. 
