Ixii 



INTRODUCTORY AND HISTORICAL. 



thirds of its whole amount. His estimated distance of the sun was 3,592 earth's semi-diameters,* 

 bat, for the roundness of the number, he adopted 3,600, corresponding to a parallax of 49". 



Godefridus Wendelinus, (Godfrey Wendelin,) a Belgian astronomer, deduced, in 1647, from 

 morning and evening observations of the moon, f the value of the solar parallax as 15" at the 

 outside, or the distance at least 13,740 terrestrial semi-diameters, and fixed 14,656 of these 

 semi-diameters as the most probable value. Ricciolus, rejecting this comparatively small value, 

 arrived at the conclusion, J in 1665, that a value between 28" and 30" could deviate only by 

 very few seconds from the truth. 



Bicciolus gives an interesting list of the successively adopted values, a tabular view of 

 which is as follows, the references having been verified or corrected in all cases where I have 

 access to the originals, which has been generally the case, and in some instances made more 

 complete. 



Distance of the sun from the centre of the earth, expressed in terrestrial semi-diameters. 



[1] 8M LtuiDi-i TraiU d' Mrmomit II. 403, 3. [8] SIM JUne nimjaU Cnuorimu dt die nataU 13. Billig. Plmiiu I, 129. 



[3] EICCIOLI, Lit. HI, ScAo/. II, p. 111. 



The next attempts at determining the parallax were those of Cassini and Richer. The latter 

 astronomer was sent by the French Academy to South America for purposes similar to those 

 which prompted in our days this present expedition of Lieutenant Gilliss. His observations 

 were published]] in 1679, after his return, and his declinations of Mars were compared by 



Ibid , p. 456. 



t RIOCIOLI Almaf*hm Novum, I, 109, 731. WEIDLTE Hal. A*r. p. 457. See also his letter GAMINDI Op.amn. VI, 464. 

 t Ktociou Aim. Aw., I, 110, 731, 734. 



fCf. PuTAica dcpladtu PHbnpkKw* lib. II, cap. 31. Arirtarchus Propos. 7. 



| OtunaHau alnnamiyna ttpkyritpu, fata en t Ut dt Cayenne, par M. Rionia, Parig, 1679. Also Mtm. dt VAead. Roy. da 

 VII, PI l.p. J33. 



