194 CELESTIAL MEASURINGS AND WEIGHINGS. 



ring (which they do in a very leisurely manner), leaving 

 the apparent displacement of the planet on the sun's disc 

 to subsequent calculation, on a comparison of reports 

 from all the points of observation selected. One-fourth 

 of the advantage arising from its proximity, it is true, \\ 

 lost, by the sun itself sharing to that extent in the dis- 

 placement of the planet ; but enough remains to give 

 this a superiority over every other method of measuring 

 the sun's distance. 



(i8.) Taking as the general conclusion for that dis- 

 tance which we must at present rest in, that assigned in 

 our article last cited, viz., 91,718,000 imperial (or 

 91,626,282 geometrical) miles, we find it equivalent to 

 23,222 polar semi-diameters of the earth, or ten million 

 times that number of geometrical cubits of twenty-five 

 pwmetrical inches each. 



o 



(19.) Our next step is to the fixed stars, within whose 

 sphere modern science has at length made good a foot- 

 ing, secure, tliough somewhat unsteady for the present. 

 In conformit) with the same principle of procedure, we 

 here rest for our base of operations on our last and 

 greatest accessible measured length, viz., the diameter of 

 the earth's annual orbit, a base line of 183,000,000 miles, 

 which, as the orbit is very nearly circular, presents itself 

 (in some situation or other across it) perpendicularly to 

 a line joining the sun and any selected star, so as to be 

 seen unforeshortened from the .star. As the earth at 

 half-yearly intervals passes alternately from one to the 

 other extremity of such a diameter, the visual line by 



