Ij6 TABLE 164. 



TERTIARY STANDARD WAVE-LENGTHS. IRON ARC LINES. 



For arc conditions see Table 160, p. 172. For Hnes of group c class 5 for best results the 

 slit should be at right angles to the arc at its middle point and the current should be reversed 

 several times during the exposure. 



* Measures of Burns. t Means of St. John and Burns. 



J Means of St. John and Goos. Others are means of measures by all three. References : St. John and Ware, 

 Astrophysical Journal, 36, 1912; 38, 1913; Burns, Z. f. wissen. Photog. 12, p. 207, 1913, J. de Phys. 1913, and unpub- 

 lished data; Goos, Astrophysical Journal, 35, 1912; 37, 1913. The lines in the table have been selected from the 

 many given in these references with a view to equal distribution and where possible of classes a and b. 



For class and pressure shifts see Gale and Adams, Astrophysical Journal, 35, p. 10, 1912. 

 Class a: "This involves the well-known flame lines (de Watteville, Phil. Trans. A 204, p. 139. 

 1904), i.e. the lines relatively strengthened in low-temperature sources, such as the flame of the arc, 

 the low-current arc, and the electric furnace. (Astrophysical Journal, 24, p. 185, 1906, 30, p. 86, 



pressure are assigned to it for the present. These are bright and symmetrically widened under 

 pressure, and show mean pressure displacements of 0.009 Angstrom per atmosphere for the lines 

 in the region \ 5975-6678 according to Gale and Adams. Group c contains lines showing much 

 larger displacements. The numbers in the class column have the following meaning : i, sym- 

 metrically reversed ; 2, unsymmetrically reversed ; 3, remain bright and fairly narrow under pres- 

 sure ; 4, remain bright and symmetrical under pressure but become wide and diffuse ; 5, remain 

 bright and are widened very unsymmetrically toward the red under pressure." 



For further measures in International units see Kayser, Bericht iiber den gegenwartigen 

 Stand der Wellenlangenmessungen, International Union for Cooperation in Solar Research, 1913. 

 For further spectroscopic data see Kayser's Handbuch der Spectroscopie. 



SMITHSONIAN TABLES. 



