. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. ON ASTRONOMY. 93 TugS y A In 1750 Boscovicli and Le Maire measured an arc from Eome to Rimini, a distance of nearly 140 miles. In 1752 Liesganig measured an arc passing througli the observatory of Vienna, and about the same time Beccaria measured another in the plains of Lombardy. In 1764 Charles Mason and Jeremiah Dixon measured a line of about 100 miles in length along the valley of the Delaware. They were engaged at the time in running t
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. ON ASTRONOMY. 93 TugS y A In 1750 Boscovicli and Le Maire measured an arc from Eome to Rimini, a distance of nearly 140 miles. In 1752 Liesganig measured an arc passing througli the observatory of Vienna, and about the same time Beccaria measured another in the plains of Lombardy. In 1764 Charles Mason and Jeremiah Dixon measured a line of about 100 miles in length along the valley of the Delaware. They were engaged at the time in running the boundary line between the States of Pennsylvania and Maryland, and finding a finelocality for measuring an arc of the meridian, they informed the Royal Society of London of the fact and offered to execute the work if the Society would iurnish the requisite instruments. The Society, under the advice of Dr. Mas- kelyne, the astronomer royal, gladly accepted the offer of Messrs. Mason and Dixon. This line is re- markable as having been actually measured through its whole extent with wooden rods,or rather a wooden frame, sent out for the purpose by the Royal Society. It was made of fir, 20 feet long and 4 feet wide, with adjustments for being leveled by plumb line. This measurement has always been regarded as a very ac- curate one. The latitude of the middle point of the line is 39° 12' nearly. This arc is one of the 13 used by Airy in determining the figure of the earth. 10. After the peace 1783 Cassini de Thury addressed a memoir to the Royal Society of London upon the importance to astronomy of deter- mining more accurately than had before been done the difference in longitude between the observatories of Paris and Greenwich. The suggestion was favorably received and commissions were appointed by both governments to carry the project into effect by a trigonometrical survey. General Roy was at the head of the English commission.^ The French operations were committed to Count
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