38 



ASTRONOMY. MASKELYNE DELAMBKE. 



[Diss. VI. 



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. 



(162.) In France, after the death of the celebrated La- 

 Lalande. caille, 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 Abbe Outhier alone, it is said, knew how 

 to use a quadrant, and the celebrated Lagrange was 

 as ill informed until instructed by Lalande. 1 

 (163.) But the most important labours of the French 

 French arc astronomers at the close of the last, and at the com- 

 of the me- mencement of the present century, were in carrying 

 out the measurement of the arc of the meridian from 

 Dunkirk to the Balearic Isles, with the more imme- 

 diate object of fixing the length of the metre, but con- 

 tributing to the solution of far more considerable pro- 

 blems connected with the FIGURE 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 Mechain, Biot, and Arago. 

 (164.) DELAMBRE 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 

 ^ 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 in whom 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 formulas. 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- 

 tween the merits of French and British astronomers. 



talents 



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 Terns between 1788 and 1817. 



Of his original labours the measurement of the 

 French Arc of the meridian, of which he hasgivenafull th g p^Lch 

 account in his Base du Systeme Metrique Decimal, is Arc. 

 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 measm-e, which it was proposed should 

 be done by a joint committee of the Royal Society 

 and the French Academy. 2 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 Mechain 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 

 arc was afterwards extended to Formentera in the 

 Balearic Isles, and the whole length of the arc 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- (166.) 

 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, 





difficul- 



1 Both anecdotes are told by Moll, who had them from Delambre. 



2 The two governments and their respective learned societies had already co-operated in 1784 for a survey to connect 

 Paris and Greenwich Observatories. 



