The Spectrum of 77 Argus. 



Eleven selected iron lines were carefully measured with the Toepfer 



micrometer. A least-square solution with Hartmann's formula gave 



(*o) (C) 



X = 2180-30 - 181854 ' 2 

 n - 128-8971 



Oo) 



of which the residuals respectively were 



A. 



Kesid. 



X. 



Resid. 



4063-72 



-0-03 



4404-79 



-0-15 



4171-82 



-0-02 



4476-34 



0-15 



4118-90.... 



0-18 



4529-1 



0-30 



4143-85 



-0-16 



4872-25 



0-35 



4260-61.... 



. -0-06 



4957-50 



-0-18 



4325-88 



. -o-io 







In determining the wave-lengths of the lines in the spectrum of 

 7; Argus the above formula was not used, as the representation did not 

 seem sufficiently exact nor could the whole spectrum be conveniently 

 measured at once. 



The attached table shows the subdivisions of observation and com- 

 putation. The above value of A was retained in the computations, 

 but n and C were determined separately for each block. The means 

 of the micrometer readings are corrected for the carefully determined 

 errors of the screw. 



It will be noted that we get for the wave-lengths of the hydrogen 

 lines the following results : — 



Observed. Known. K — O. 



Hp 4863-38 4861-49 - 1-89 



H y 4343-71 4340-66 -3-05 



H 4105-08 4101-85 -3-23 



As there is no symmetry between the time of exposure of the plate 

 to the iron flash and to the star-spectrum, we cannot suppose this 

 displacement to be necessarily due to motion of the star ; it is more 

 probably due to change of temperature, &c, in the spectroscope. The 

 wave-lengths given in the separate column are corrected for displace- 

 ment so as to bring out the wave-lengths of the hydrogen and other 

 lines at their true values. 



The wave-lengths of the corresponding bright lines in the spectrum 

 of Nova Aurigae as observed at the Lick Observatory or Potsdam,' 55 ' are 

 given in the adjoining column, and the agreement is very remarkable. 



The photograph with the object-glass prism was taken in 1899, 

 January 14, with an exposure of one hour. The star was trailed to 

 and fro for 0*5 mm., the guiding being done by a neighbouring star 

 viewed in the guiding telescope. The original negative is enlarged 

 5 diameters in the plate sent (fig. 2, Plate 4). 



* Schemer's (Frost) ' Astronomical Spectroscopy/ p. 287. 



VOL. LXVII1. 2 K 



