OF ARTS AND SCIENCES. 



275 



Argentina is 6.5, corresponding to a photometric magnitude of 6.3. 

 This value, altliough reducing the discrepancy, would still make the 

 variable 6.5, which is 0.7 fainter than its light at minimum. This 

 comparison is not given in the catalogue of Ilerschel, and accordingly 

 is not checked by appearing under both 2 and 3 Sagittarii. 



The southern declination of the star restricts the time of obser- 

 vation within narrow limits. The star sets at 9'*, and twilicfht would 

 not be over until about 7"^. Accordingly, the time of observation 

 would be 1795, Sept. lo-i 8'' ± 1\ The elements of Schonfeld* give 

 a minimum at 1795, Sept. 15'* 16^ for Ep. —3902. The period of 

 Schmidt,! on the other hand, gives 1795, Sept. 13*^ 22''. If, then, the 

 star was really at its minimum when observed by Herschel, this obser- 

 vation determines a correction to the period with great certainty. 



8 Lihrce. — The observations of this star are so important that they 

 require a more detailed discussion. The law of variation of the light 

 has been determined by Professor Schonfeld.t Table III. gives the 

 names of the various comparison stars, the letters by which they are 

 designated by Professor Schonfeld, and the brightness in grades that 

 he assigned to them. The next columns give the light according to 

 the photometric measures made at this Observatory, and according 

 to the Urauometria Argentina. The grades are reduced to magni- 

 tudes, as described on page 271, according to each of the scales. The 

 results found by subtracting the magnitudes derived from the grades 

 from that given in the two catalogues are given in the last two 

 columns. 



TABLE III. 



The light of the variable at maximum and minimum equals 13.0 

 and 2.0 grades respectively. This corresponds to a variation from 

 4.9 to 5.8 on the photometric scale, and from 5.5 to 6.4 on the scale 

 of the Uranometria Argentina. 



The observations of Sir William Herschel are compared in Table IV. 



* Zweiter Catalog. 



X Astron. Nach., Ix.xiv. 312. 



t Astron. Nach., Ixxxvii. 109. 



