1824.] Account of 



Cassiiii de Thuiy, Director of t!ie Royal 

 Observatory, tlic son of jHCfjties, and 

 grandson of tiie first Cassini, who, at the 

 a^e of ten, had calculated tlic entire 

 phases of the snn for 1727, and had heen 

 admitted into the academy at the age of 

 21, conceived the project of that chart 

 of France to wiiicii lie has given ids 

 name. For the basis of his labour, lie 

 proposed to subject all the distances, 

 and to refer all tiie clL-nieuts, to the 

 simple idea of the theory of co-ordi- 

 nates ; this consists in tracing, on the 

 earth, two great perpendicular lines, one 

 from north to south, the other from east 

 to west, and divided into equal jjarts of 

 00,000 toisi's eacL, by lines parallel to 

 one another, setting out from their point 

 of intersection at the Observatory. 



This chart, commenced about 1750, 

 by order of Louis XV. under the direc- 

 tion of Cassirn de Thnry, was carried on 

 by his son, Cassini IV. whose survey 

 was compleled about 1787, three years 

 after the death of its principal author. 

 It consists at present of 182 sheets or 

 numbers, is engraved on a scale of from 

 1 to 80,400, and finnishcs all the details 

 that a seinitopography will admit of. 



Cassini de 'i hury superintended the 

 execution of tiiis vast undertaking 

 during forty years, or from 1744; when, 

 with (he aslroirotner Maraldi, tiie se- 

 con<l ol' the name, they constructed and 

 published the chart of the great trian- 

 gles which have served as a l'oun<!ution 

 and regulators of the more minute ope- 

 rations. Jacques Dominic Cassini, great 

 grandson of the famous astronomer, and 

 now a member of the Institute, &e. car- 

 ried it on from the death ot his lather, in 

 1784, ten years additional, bringing it 

 towards a close in 1793; there only 

 remained, then, to complete it entirely, 

 three plates to be engraved. All the 

 sheets of this noble spcein)cn of geodesy, 

 arising from the divisions of the total 

 surliice of I'ranre, made by thirteen 

 parallels to llic meridian from east to 

 west, cut by t\»enty perpendiculars from 

 north to south, to this same meridian ; 

 all these may be combined so as to form 

 one single map, which would compre- 

 hend a space of about tiiirty-six feet 

 square. Each sheet or nundier foiming 

 a parallelogram, represents 40,000 toiscs 

 ol breadth by 25,000 of Ic^nglh, and a 

 Kinface of l,U0U,0t)O.(J00 of squaic 

 toises. To give an idea, still more 

 complete, of the immensity of these 

 labours, it may be slated, that thirty- 

 seven years were occupied in their 

 execution, under the direction of tiic 



the Cassi7iis, 



397 



Cassinis, that thirty engineers were cm- 

 ployed for the small triangnlation and 

 the details, and that their labours called 

 for 400 original drawings, 50,000 copies 

 of tables of distances from the meridian, 

 60 volumes of observations and registers 

 of engineers, 600 stitched books of cal- 

 culations, and 500 ditto of the enumera- 

 tion of communes. 



It was the perseverance of Cassini de 

 Thury that overcame all obstacles; he 

 had to struggle with numberless discou- 

 ragements, from the secondary agents 

 employed under him, and at times with 

 a scarcity of the requisite pecuniary 

 means. Public opinion in France has 

 assigned to him the title of Creator of 

 Topography. 



Cassini had projected a geometrical 

 description of all Europe, on the model 

 of that of France; he began, at Stras- 

 burgh, a triangnlation which was to 

 terminate at Vienna, and cover the 

 German empire. He met with encou- 

 ragement at first ; but, certain princes 

 of the empire not feeling a like interest 

 in it, his farther progress was obstructed. 



Prior to this map, France possessed 

 critical, but not geometrical, geography. 

 Or, at least, the exceptions nnist be 

 confined to the map of the Pyrenees, 

 by Roiissel, and to some other particu- 

 lar maps and plans of battle. New 

 instruments have been invented, and the 

 geodesic mcliiods have attained greater 

 perfection ; but, considering the extent 

 represented, liiis map maintains its pre- 

 eminence, and will do so till the new 

 general topographical map, intended for 

 all the public services, and confitled to 

 the Royal Corps of Gcograpineal Engi- 

 neers shall be completed. This last 

 was ordered by the present king in 

 1817. 



The family of the Cassinis, to wlioni 

 (ho Map of France is owing, has been 

 truly astronomical and geographical, 

 from father to son; numerically, they are 

 de.signatid by the names of Cassiid the 

 first, second, third, and fourth. The 

 two astronomers Maraldi, who were 

 associated with the four Cassinis in the 

 Rojal Observatory, anil who made 

 astronomical observations, without in- 

 terruption, through a scries of 122 years, 

 were of the Cassini family. John Do- 

 minic, (he first Cassini, took possession 

 of the Observatory Sept. 14, 1671, the 

 day when the building was finished ; 

 and in 1793, Jaques Dominic, the last 

 Cassini, director of the establishment, 

 (piitted tin; scientific residence of his 

 fathers. Jaques Philij)pe Marahli, who 

 CO operated 



