SECTION II. 



ASTRONOMICAL EXPEDITION TO CHILI DURING THE YEARS 

 18491852. 



IN the year 1847, Dr. C. L. Grerling, a distinguished 

 mathematician of the Marburgh University, suggested 

 the importance of a new determination of the sun's 

 parallax by observations upon Yenus at and near her 

 stationary periods. The determination of the dimensions 

 of the solar system rests entirely upon the assumed 

 value of the sun's parallax. The value now generally 

 received, viz., 8*.57, rests upon the observations of the 

 transit of Yenus in 1769. Transits of Yenus over the 

 sun's disc afford the best method of determining this 

 parallax; but these phenomena are of very rare oc- 

 currence, there being not a single transit visible in any 

 part of the world from 1769 to 1874. Now, although 

 the observations of the transit of 1769 are believed to 

 have afforded a very accurate value of the sun's parallax, 

 yet it is much to be regretted that the results obtained 

 by combining the observations at different stations two 

 and two, differ among themselves by an entire second. 

 It is therefore very desirable that this result should be 

 verified by independent methods. Such methods are 



