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 indireet 
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 Pingré, at the Isle of St. Domingo 
by Fleurin, at California by the Abbé 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, 
&e. 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 Promota, 1663).— Translator. 
