ASTRONOMY AND METEOROLOGY. 313 



observations, differential methods will probably be employed, in- 

 asmuch as the time now assigned for my absence from home 

 would be inadequate for proper discussion of the correction re- 

 quired for nice determinations of an absolute character. Still, it 

 is my present purpose, so far as possible, to make such subsid- 

 iary determinations as might hereafter be needed in any attempt 

 at computing the observations absolutely. But as I hardly ven- 

 ture to anticipate any opportunity of making a thorough deter- 

 mination of the constants of refraction, or of the errors of gradu- 

 ation, it seems best to arrange for a differential computation at 

 least at first. It is improbable that a sufficient number of well- 

 determined stars will be found available even for this differential 

 reduction, and the necessity may thus be entailed of determin- 

 ing the comparison-stars myself, this determination, however, 

 itself depending upon standard star places. So far as possible I 

 propose employing those heretofore determined by me, and pub- 

 lished by the Coast Survey, which form the basis of the star 

 places of the American ' Nautical Almanac.' With these obser- 

 vations of position it is my hope to combine others of a physical 

 character to some extent ; but in the presence of a plan implying 

 so much labor and effort, it would be unwise to rely upon the 

 possibility of accomplishing much more than the zone-work. The 

 meteorological relations of the place are very peculiar; but I dare 

 not undertake any connected series bearing upon these, without 

 self-registering apparatus, which is beyond my means. Cor- 

 dova is one of the oldest cities, and contains the oldest university, 

 of the Western Hemisphere. It is situated in 31 S. latitude, 

 on the boundary of the Pampa, where the land begins to rise 

 towards the group of mountains known as the Sierra de Cordova. 

 It is connected with Rosario, on the Parana, by the Central Argen- 

 tine Railway, which has probably been already opened to travel 

 through its entire length of about 280 miles, although information 

 to that effect has not yet reached this country. The two largest 

 instruments will be a Repsold meridian-circle'of 54 inches' focal 

 length, and 4 inches' aperture, and an equatorial, by Alvan Clark 

 and Sons, provided with the 11-inch object-glass, by Fitz, lately in 

 the possession of W. Rutherfurd, who has supplied its place by 

 one of 13 inches. A photometer, by Ansfeld, of Gotha, according 

 to Zb'llner's latest form, has been constructed under the super- 

 vision of Professor Zollner himself;- a spectroscope will be fur- 

 nished by Merz, of Munich, and a clock by Tiede, of Berlin. The 

 scientific institutions of the United States have afforded the expe- 

 dition every possible assistance. The Coast Survey lends a 

 circuit-breaking clock, a chronograph, and a portable transit; the 

 Smithsonian Institute lends a zenith telescope; the American 

 Academy of Arts and Sciences, of Boston (probably), a photom- 

 eter and spectroscope ; the Washington Observatory and the 

 Nautical Almanac ' have greatly aided the undertaking by gifts 

 of books, and by a manuscript copy of Gilliss's ' Catalogues of 

 Standard Stars;' and from the astronomers of England, Ger- 

 many, and Russia, important assistance has been freely and 

 effectively contributed, in the order and supervision of instru- 



