INTRODUCTORY AND HISTORICAL. 



and widely remote points, which was not the case in 1761. Finally, an eclipse of the sun 

 followed close after the transit, affording an excellent opportunity for fixing the longitudes of 

 the places of observation. 



No exertions were spared by the votaries or protectors of astronomy for obtaining numerous 

 and accurate observations, and as Encke has said,* with as much truth as delicacy, " whatever 

 may be the future judgment as to the actual issue, posterity will never be able to reproach 

 either the astronomers or the governments of that period with having neglected to call sufficiently 

 careful attention to the more important points, or with having failed to further and support 

 scientific efforts with sufficient readiness." No one will deny that the enlightened aid of 

 national resources, and the generous enthusiasm of astronomers, were alike necessary for pro- 

 viding those materials which, in the hands of the illustrious astronomer of Berlin, have furnished 

 the definite value with which the world has been amply content for more than a quarter of a 

 century, and which may not impossibly remain the standard for a quarter of a century to come. 



The observations and disquisitions called forth by this rare and now peculiarly important 

 phenomenon are far too numerous for full citation. f The chief observations were collected by 

 Lalande in a treatise, J from the abundant works in which they were made public, and these, 

 with such as had been omitted there, are given in full detail in Encke' s classic investigation of 

 this transit. 



The value of the parallax found by different astronomers from this transit of Venus are con- 

 fined within much narrower limits than those from the former. The smallest was Planmann's, 

 8". 43 ; the largest Pingre's, 8".81, and Euler's, 8". 82 ; Hornsby found 8". 78, Lalande 8".50, 

 Lexell 8".68, Smith 8".605, Maskelyne 8".723. 



The observations were subjected by Ferrer, in 1808, to a discussion, from which he obtained 

 the value 8".615;|| and in 1815 to a very thorough investigation, posthumously published^ in 

 1832, and giving** 8".577 i 0".3 as the result. 



Meantime, however, had appeared the two books of Encke, already quoted ; the first published 

 in 1822, containing an ample scrutiny of the observations of the transit of 1761, June 6, and 

 deducing the final value 8".49050".607 ; and the second, published in 1824, giving a thorough 

 criticism and discussion of the transit of 1769, June 3. In this latter he determines the amount 

 of certain corrections, necessarily disregarded in the first treatise, and finally adopts the following 

 results as final for the solar parallax. 



From the transit of 1761 8".5309 0".0623. 



1769 8".6030 0".0460. 



From the two together 8".5776 0".0370. 



Connected with the transit of 1769 are some circumstances which, from their historical 

 importance, demand some allusion here. One of the most important points for the accuracy of 

 the determination was the station at Fort Wardoehuus, on Wardoe, an island in the Arctic 

 ocean, at the northeastern extremity of Norway. To this point the Danish government had sent 

 a clergyman of Vienna, Father Hell, with two assistants, Sainovicz and Borgrewing. Numerous 

 circumstances tended to throw suspicion on Hell's observations, which he had suppressed for 

 nine entire months, regarding which he had repeatedly seemed to prevaricate, and which, when 



Venusditrchffang von 1769, 1. 



t Sufficient are the following memoirs: 



RITTENIIOCSB, Trans. Am. Phil. Soc. I. p. 89. SMITH, Trans. Am. Phil. Soc. I, p. 162. App. p 54. 



LALANDE, Mfm. de I'Acad. 1770, p. 9 ; 1771, p. f76. HORNSBY, Phil. Trans. 1771, p. 574. 



PiNGRE,J/i?m. del'Acad. 1770, p, 558; 1772, p. 398. LEXELL, Vetenskaps. Akad. llandl. 1771, pp. 200, 301. 



MASKELYNE, Phil. Trans. 1768, p. 55 ; 1769, p. 414. EULEB, Phil. Trans. 1772, p. 69. 



MASKELYXE, Trans. Am. Phil. Soc. I, p. 4. App. p. 1. PLANMANN, Vetenskaps. Akad. Handl. 1772, pp. 183, 358. 

 J LALANDE, Mtmoire sur le Passage de Vfnus absent k 3 Juin, 1769, Paris ; 1772. 

 Der Vtnusdunhgang van 1769, Sfc., bearbeitel von 3. F. ENCKE, Gotha ; 1824. 

 ||Proc. Am. Phil. Soc. VI, p. 355. ^Mem. R. Ast. Soc. V, p. 253. 



o Mem. R. Ast. Soc. V. pp. 2. r >4, 282, 295. 

 K o 



