(163.) 
836 
pose of ascertaining whether no planetary body filled 
the void between Mars and Jupiter. To Piazzi, of 
Palermo, we owe a most excellent catalogue of fixed 
stars from observations with a moveable circle of 
four feet radius by Ramsden. Oriani of Milan was 
likewise one of the best informed practical astrono- 
mers of his time. 
In France, after the death of the celebrated La- 
eaille, perhaps Lalande (who was exactly Maskelyne’s 
contemporary) was the most active astronomer. To 
him and his nephew we owe a very valuable catalogue 
of 50,000 stars, lately edited by the British Associa- 
tion. But practical astronomy was seriously neglect- 
ed in France generally. The national observatory 
was feebly superintended by the later members of 
the Cassini family; of the French expedition under 
Maupertuis to measure the length of a degree in Lap- 
land, the Abbé Outhier alone, it is said, knew how 
to use a quadrant, and the celebrated Lagrange was 
as ill informed until instructed by Lalande.* 
But the most important labours of the French 
French arc astronomers at the close of the last, and at the com- 
of the me- 
ridian. 
(164.) 
mencement of the present century, were in carrying 
out the measurement of the are of the meridian from 
Dunkirk to the Balearic Isles, with the more imme- 
diate object of fixing the length of the métre, but con- 
tributing to the solution of far more considerable pro- 
blems connected with the FicuRE oF THE EARTH. We 
connect this labour with the respectable name of De- 
lambre, who was more intimately associated with it 
than perhaps any other person, though united with 
such eminent men as Méchain, Biot, and Arago. 
Detamerz was the pupil of Lalande, who used to 
Delambre ; say that his disciple was his best work. He first ob- 
his charac- tained distinction as a computer of tables. Those of 
ter and 
talents, 
the motions of the Sun, Jupiter, Saturn, and Uranus, 
and of the satellites of Jupiter were deservedly 
prized, and some of them are still the best of their 
class. He was a man inwhom the love of truth and 
accuracy was conspicuous. Learned and patient, he 
spared no pains in acquiring knowledge, and in using 
it to the best purpose. As a calculator he was emi- 
nent. Physical astronomy he did not cultivate, ex- 
cept with a view to compare its deductions with facts. 
He was intimately conversant with all properly as- 
tronomical methods and formule. He knew the his- 
tory of every problem, and the details and modifica- 
tions of every astronomical instrument. He has 
embodied the results of this vast industry in a series 
of works (forming six quarto volumes) on the his- 
tory of his favourite science, which are without a 
parallel for fulness and impartiality. He laboured 
as conscientiously to ascribe the due credit to Hip- 
parchus and Ptolemy as to hold an equal scale be- 
iwveen the merits of French and British astronomers. 
ASTRONOMY.—-MASKELYNE—DELAMBRE. 
(Diss. VI. 
His critical knowledge of the ancient languages (for 
he could speak Greek with fluency) was not more re- 
markable than his complete freedom from national 
prejudices. Both attributes qualified him pre-emi- 
nently for the office of an historian. He published 
also a large treatise on astronomy, and numerous 
memoirs on practical subjects in the Connaissance 
des Tems between 1788 and 1817. 
Of his original labours the measurement of the 
French Arc of the meridian, of which he has givenafull 
account in his Base du Systéme Métrique Decimal, is 
the most important. As some account of this un- 
dertaking has been given in Sir John Leslie’s Dis- 
sertation, I shall state concisely a few particulars not 
there mentioned. Not the least singular feature of 
this gigantic work was the political crisis under 
which it was conducted. So early as August 1790, 
the French Constituent Assembly, on the motion of 
Talleyrand, desired the king to write to the English 
government, to represent the advantage of the two 
nations uniting to adopt a common unit or standard 
of weight and measure, which it was proposed should 
be done by a joint committee of the Royal Society 
and the French Academy.? This application was 
probably never made, at least nothing came of it; 
but the Academy named their own committee, who, 
after discussing three sorts of natural standards,— 
the length of the pendulum in lat. 45° (first proposed 
by Huygens in his Horologium Oscillatorium), the 
length of a quadrant of the equator, and that 
of a quadrant of the meridian from the equator to the 
pole assumed to be elliptic,—adopted the latter, 
and this labour was committed to Méchain for the 
southern part, from Rodez to Barcelona (170,000 
toises), and to Delambre for the northern, from 
Rodez to Dunkirk (380,000 toises). The southern 
are was afterwards extended to Formentera in the 
Balearic Isles, and the whole length of the are was 
found astronomically to be 12° 22’ 12"6. Two bases 
were measured (both by Delambre), one at Perpignan 
of 6006 toises, the other at Melun of 6076 toises 
(each about 7°3 miles). When the length of the for- 
mer was computed by triangulation from the latter, 
the difference of the observed and inferred amount is 
said to have been only ten or eleven inches. 
But difficulties greater than physical obstacles pre- 
sented themselves to the completion of this vast work, 
The excited state of the public mind during the most 
frenzied period of the French Revolution rendered 
the simplest operations matters of suspicion. The 
nearer to Paris that the survey was carried on, the 
greater were the precautions necessary. Instruments 
were seized, assistants arrested, and night signals had 
to be totally dispensed with. ‘The coolness and in- 
trepidity of Delambre, added to unexampled patience, 
1 Both anecdotes are told by Moll, who had them from Delambre. 
? The two governments and their respective learned societies had already co-operated in 1784 for a survey to connect 
Paris and Greenwich Observatories, 
165.) 
History of 
the French 
Are. 
(166.) 
Its difficul- 
ties. 
