334 LAPLACE. 



errors in the direction of the visual lines exercise an 

 enormous influence upon the results. 



In the beginning of the last century Halley remarked 

 that certain interpositions of Venus between the earth 

 and the sun, or, to use an expression applied to such 

 conjunctions, that the transits of the planet across the 

 sun's disk, would furnish at each observatory an indirect 

 means of fixing the position of the visual ray very su- 

 perior in accuracy to the most perfect direct methods.* 



Such was the object of the scientific expeditions un- 

 dertaken in 1761 and 1769, on which occasions France, 

 not to speak of stations in Europe, was represented at 

 the Isle of Rodrigo by Pingre, at the Isle of St. Domingo 

 by Fleurin, at California by the Abbe Chappe, at Pon- 

 dicherry by Legentil. At the same epochs England sent 

 Maskelyne to St. Helena, Wales to Hudson's Bay, Mason 

 to the Cape of Good Hope, Captain Cooke to Otaheite, 

 &c. The observations of the southern hemisphere com- 

 pared with those of Europe, and especially with the ob- 

 servations made by an Austrian astronomer Father Hell 

 at Wardhus in Lapland, gave for the distance of the sun 

 the result which has since figured in all treatises on as- 

 tronomy and navigation. 



No government hesitated in furnishing Academies with 

 the means, however expensive they might be, of conven- 

 iently establishing their observers in the most distant 

 regions. We have already remarked that the determi- 

 nation of the contemplated distance appeared to demand 

 imperiously an extensive base, for small bases would 

 have been totally inadequate to the purpose. Well, 



* The utility of observations of the transits of the inferior planets 

 for determining the solar parallax, was first pointed out by James 

 Gregory ( Optica Promote, 1663). Translator. 





