\vi ORIGIN AND OPERATIONS 







cient aid in its promotion. It has been proposed by one of known zeal, industry, ami ability 

 in astronomical observations, wh ts will not bo wanting to bring it to a suc- 



cessful issue. 



The plan is one which emanated from Dr. Oerling, of Marburg, well known for his astro- 

 nomical and geodetical labors, ami communicated by him in a letter to Lieut. Gilliss, dated 

 April 17, 1847, in which he earnestly seeks for it the co-operation of American astronomers. It 

 contemplates two aeries of observations, each hearing upon the question of parallax, but in dit- 

 ferent ways, and independently of each other. One series is to be made with meridian instru- 

 ments, at stations as remote from each other in latitude as practicable, and will consist of 

 differential measurements in decimal inn between Venus and the brighter stars near its path, 

 which are visible in the daytime. To render these available in the question of parallax, flic 

 distance K-tween the observatory at Washington and the preposed station at Chile will afford 

 an ample base of 6,000 miles. The other series embraces differential observations out of the 

 meridian, more particularly in right ascension, and which, in cases of the planet's near ap- 

 proach t Mr, can be made with the utmost nicety. A few instances of near approac! 

 some of the brighter stars may be selected, when the two bodies can be followed throughout the 

 day. And. in such case, full series of observations, with a well-mounted equatorial instrument, 

 would be among the most valuable for the proposed object, and their value would be increased 

 bj combinations with others of a similar kind at other and remote stations. 



" For such observations it is proposed to occupy some point in Chile as an astronomical station. 

 So far as they may be available in the determination of the solar parallax, or even for the con- 

 firmation of previous determinations, they will be of the highest interest. But, apart from this 

 primary object, the expedition and the observations contemplated commend themselves upon 

 other grounds to the warm interest of all astronomers and lovers of science. The perfection of 

 -e observations will require others upon other objects, and the whole will he a just tribute of 

 America and American astronomers to their co-laborers in a science to which our country is 

 largely indebted for the prosperity of some of its most important interests. No such expedition 

 has ever returned without rich fruits, even of different kinds, and gleaned from different fields 

 from those for which it was originally designed. 



" The fact that a quantity so essential to our accurate knowledge of the solar system as the 

 son's parallax should rest for its determination mainly upon observations of a single phenom- 

 enon the transit of Venus in 1769 is sufficiently indicative of the necessity and high value of 

 the proposed measure. So important for this purpose, in the eyes of astronomers, were deemed 

 this transit and the previous hut inferior one of 1761, that we find them scattering themselves 

 over all parts of the habitable globe, wherever the phenomenon could be advantageously ob- 

 served. In 17'''1 they occupied stations from the remotest regions of Siberia to the southern 

 i-mity of Africa, in the wilds of Arabia, and on the islands of the Indian sea. In 1769, 

 with even greater zeal, they scattered over Europe, America, and the South Sea islands, to 

 observe one of the rarest, most interesting, and important phenomena which the annals of 

 astronomical science afford. Not only the learned societies, but the governments of Europe, 

 encouraged and aided the laudable undertaking. And, even in that day, American astrono- 

 mers shared in the labors, and reaped their portion of the honors of the great occasion; yet the 

 zeal of all was not rewarded with success. Unfavorable weather at some of the most important 

 stations either seriously impaired or entirely prevented observations. At others the observa- ' 



i>ecn regarded with suspicion, or as deserving little conlidence. And the distin- 



gui who has given the most thorough and scrutinizing discussion of all these obser- 



although he assigns to his resulting parallax the small probable error of 0".05, yet, near 



f his admirable treatises on the subject, remarks that, 'bad the weather been 



fav 'lie nortl tlOW in 17l'>'.l, and had as many astronomers stationed 



theniM-lves at different points of the Friendly islands, their sixteen observed durations alone 



would have afforded a more accurate determination of the parallax than the whole 250 equations 



