ASTRONOMY. 185 



This is the first astronomical publication of the national observatory of 

 the Argentine Eepublic. 



One of the first objects of Dr. Gould, on the establishment of the 

 new observatory in 1870, was the makingof a uranometry of the southern 

 sky, wliich should contain the position unci magnitude of every star 

 visible to the naked eye at his station. 



The model on which it is made is the celebrated "Uranometria nova,-' 

 of Argelander, of Bonn, which was published in 1843. The latter 

 contains 3,256 stars from the first to the sixth magnitude, which are to 

 be seen above the horizon of Bonn. Its magnitudes are expressed in 

 thirds of a Avhole magnitude, and Argelander's scale, so established, 

 has served for a standard in all the observations in the northern hemi- 

 sphere. Dr. Gould's problem was to extend this enumeration over the 

 whole southern sky, keeping accurately to the standard set by Arge- 

 lander. This is by no means an easy task, as the minimnm rii^ibik at 

 Cordoba was found to be not the G.O magnitude, but 7.1; that is, stars 

 can still be seen at Cordoba which have less than four-tenths of the 

 light of the faintest of Aroelander's stars. This extraordinary trans- 

 parency of the atmosphere required the extension of Aroelander's 

 scale downward, and that this was accomplished successfully is shown 

 by a comparison of the magnitudes of all the stars which are common 

 to the two uranometries. The mean difference is rather less than one- 

 tenth of a magnitude. The method of settling the standard was to 

 select from the "Uranometria nova" a belt of stars which had the same 

 altitude at Bonn and at Corc'ioba. The 722 stars of this belt were ob- 

 served by the four assistants at the southern observatory (Messrs. Eock 

 Thoivie, Davis, and Hathaway), and those stars for which their esti- 

 mated magnitudes were precisely the same were chosen for standards. 

 Thus, a number of stars of each magnitude, as 3.00, 3.33, 3.06, 4,00, 4.33, 

 etc., became types to be constantly referred to. From these types a 

 number of others in a zone near the south pole (and hence constantly 

 visible) were constructed. The process of observation consisted in re- 

 ferring each star in the heavens to this set of types, so that its magni- 

 tude could be finally determined ujion. This was done by the four 

 observers independently, but often in duplicate, and so well were the 

 standards fixed that each observer's comioarisons differed from the mean 

 of all four by quantities very mucli less than a tenth of a magnitude. 

 It should be said that the magnitudes in the southern manometry' are 

 given to tenths. 



In all there are 10,649 stars visible to the naked eye at Cordoba. Of 

 these, 8,198 are as bright or brighter than the 7.0 magnitude, and these 

 alone are given in the catalogue and in the maps. Of these 10,000 stars 

 more than 40,000 observations were made. In the progress of the work 

 quite a number of variable stars were detected, of each of which a full 

 history is given in the notes. Indeed Dr. Gould's firm conviction is 



