CELESTIAL MEASURINGS AND WEIGHINGS. 189 



not, therefore, dwell on a multitude of intermediate 

 attempts between that epoch and the year 1669, when 

 Picard, under the auspices of the then newly constituted 

 French Academy of Sciences, took up the subject in a 

 truly scientific manner, and with means and appliances 

 of a higher order. They all turned, of course, as every 

 such estimate must do, on the more or less precise 

 measurement of the length of a degree or a certain number 

 of degrees of latitude on the earth's surface. But the step 

 which this measure of Picard inaugurated, is distinguished 

 by the abandonment of the old methods of ascertaining 

 such length (viz. by simply measuring it as an itinerary 

 distance by rods, or measuring chains, or by rolling 

 wheels self-registering their own revolutions) ; and sub- 

 stituting for it the infinitely more precise one, which con- 

 sists in the very careful measurement of a base line; the 

 extension from it, northward and southward, of a series 

 of triangles, as above described; the ascertaining, by 

 accurate astronomical observations, the latitudes of the 

 extreme points ; and the taking account of the deviation 

 from the true meridian of their mutual direction, by a 

 systematic process of calculation, grounded also on the 

 astronomical determination of their bearings. From 

 that to the present time, this process (in which consists 

 "geodesy" as distinct from mere mensuration and survey- 

 i ng) has been generally adopted ; with continual improve- 

 ment of the instruments used ; increasing accuracy in all 

 the requisite astronomical observations ; and the adop- 

 tion of a more and more perfect and refined system of 

 computation for the "reduction " of the observations and 



