xv i ORIGIN AND OPERATIONS 



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

 iu astronomical observations, whose personal efforts will not be wanting to bring it to a suc- 

 cessful issue. 



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

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

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

 contemplates two series of observations, each bearing upon the question of parallax, but in dif- 

 li'ivnt \v;iys, 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 declination between Venus and the brighter stars near its path, 

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

 distance between the observatory at Washington and the proposed 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 to any star, can be made with the utmost nicety. A few instances of near approach to 

 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 

 by 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 

 these observations will require others upon other objects, and the whole will be 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 

 sun'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 but 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 1761 they occupied stations from the remotest regions of Siberia to the southern 

 extremity 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- 

 tions have been regarded with suspicion, or as deserving little confidence. And the distin- 

 guished Encke, who has given the most thorough and scrutinizing discussion of all these obser- 

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

 the close of one of his admirable treatises on the subject, remarks that, 'had the weather been 

 favorable at all eight of the northern stations in 1769, and had as many astronomers stationed 

 themselves 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 



