CASSINI Dr. Tunny, C.ES no FRANCOIS, was the second son of James Cassini, and was born at Paris on the 17th June 1719. Ile received his earliest in structions in astronomy and geometry from Al. M. Ma raldi and Canms ; and when he was scarcely ten years of age, he calculated the phases of the total eclipse of the sun, which happened in the year 1727. At the age of eighteen, he accompanied his father in his two journies, for the purpose of drawing a perpendicular to the meridian of the observatory from Strasburg to Brest; and, in the year 1735, he was received into the academy as adjunct supernumerary at the early age of twenty-one.
A general chart of France having been about this time meditated, it became necessary to traverse the kingdom with several lines parallel to the meridian, and to the perpendicular to the observatory. Cassini was charged with this undertaking ; and, as the measurements taken by his father and grandfather were not exempt from er rors, he undertook to draw anew the meridian of Paris, by means of a new series of triangles, smaller in number, and more advantageously arranged, than those which had been formerly used.
A full account of this survey was published by Cassini in the Memoirs of the Academy for 1744, under the title of Meridicnne de l'observatoire de Paris veil/lee dans toutc l'etendue du royaume, par de n0uVclles observa tions,ec. avec des observations d' Ilistoire naturelle faites dans les Provinces traversees par la Meridienne. The series of triangles used on this occasion, passed along the sea coast to Bayonne, traversed the frontiers of Spain to the Mediterranean, stretched as far as Antibes, and round by the eastern frontier of France to Dunkirk. This map of triangles was terminated by two columns, on which were marked the longitude, latitude, and dis tance from Paris, of all the towns comprehended in the chain of triangles.
When the war broke out in Flanders in 1741, Cassini accompanied the king to that country, and took advan tage of this opportunity of verifying the measure of a degree by Snellius. From the materials which he had collected, he prepared a particular chart of that part of Flanders which had been occupied by the French armies, and the king was so much pleased with its accuracy, that he expressed his desire to have a chart of France pre pared in the same manner. M. De Machaud, who was then comptroller general, furnished the money which was necessary for this undertaking; but these advances were discontinued by his successor M. de Sechelles, and the King, out of regard to Cassini, announced to him personally this disagreeable intelligence. " Sire," replied Cassini, " if you will only deign to say that you view with concern the suspension of this undertaking, and that von wish for its continuance, I shall take charge of the rust." The king readily consented to this request, and Cassini immediately formed the plan of a company who should make the necessary advances, and repay themselves by the sale of the charts. This company was formed. and
Cassini had the satisfaction of seeing his great under taking accomplished. He published different works re lative to these charts, and each sheet, the number of which was 183, was accompanied with an alphabetical table, containing the distance from the meridian, and from the perpendicular, of all the different places.
These charts of France inspired the sovereigns of other countries with a desire of having their own king doms surveyed, and, in 1760, the emperor invited M. Cassini to Vienna, for the purpose of continuing to that city the perpendicular to the meridian of Paris. On the 6th of June, I-Tr'', he observed at Vienna the transit 01 Venus, an account of which he published in his en ?lllemagne, a work which contains many notices re specting the geography of the country, and the charts of Erich and Muller. Ile published a new map of that country, which represented a series of tr iangles front Strasburg to Tyrnau in Hungary.
In pursuance of his great plan, Cassini proposed to the British government to connect the general chats of France with that of the British isles. This pro posal was faN ourably received, and the trigonometrical survey of this country, of which we shall give a full ac count in another part of our work, has been carried on with the greatest ability by General Roy and General Nudge.
The attention of M. Cassini was not diverted from his astronomical studies, by the various geographical la bours in which he was engaged. He published, in 1756, additions to the astronomical tables of his father. The comparison of a great number of observations of the moon with the tables, induced him to apply another equa tion, whose period was 19 years. In 1770 he published three almanacks, which were accompanied by an univer sal instrument invented by the Prince de Conti. The pa pers which he printed in the Memoirs of the Academy., between the years 1735 and 1770, amount to 70, and are all upon astronomical subjects.
Though Cassini had naturally a strong constitution, which enabled him to undergo the greatest fatigue in the course of his geographical labours ; yet, in the latter part of his life, he was siezed with a habitual retention of urine, which rendered the last 12 years of his life par ticularly painful and distressing. In the month of Au gust 1784, he was attacked with the small pox, of which he died, on the 41.11 September, in the 71st year of his age. He left behind him a daughter, and a son, the Count de Cassini, who succeeded him in the observatory, and, till about the end of the French revolution, continued to prosecute the study of his ancestors. The pleasures of a country life, however, have drawn him from these pursuits; and his son, who forms the fifth generation of the Cassinis, has exhibited no attachment to a science with which the name of his family NVil I be for ever asso ciated. (o)