260 CARNEGIE INSTITUTION OF WASHINGTON. 



THE PRODUCTION OF CATIIODO-LITMINESCENT SPECTRA. 



Experiments were begun by Mr. King, and are now in progress with 

 the cooperation of Miss Carter, in which radiation is produced by the 

 bombardment by a stream of cathode particles of a vapor away from 

 the path of the current, the object being to obtain metalhc spectra 

 by electrical excitation alone. The preliminary experiments with 

 calcium vapor have given promising results, the hnes H, K, and X 4227 

 having been photographed, and a much richer spectrum observed 

 visually. It is hoped to extend the method to the production of other 

 metallic spectra. 



THE ZEEMAN EFFECT. 



Mr. Babcock has taken about 40 photographs of the Zeeman effect 

 for Fe, Cr, V, and Ti. The plates have yielded separations of the 

 components of 2,388 lines, most of which occur at least twice, however, 

 so that the number of new lines available is very much less than this. 

 All the values of the separations have been reduced to a standard field 

 and tabulated in order of wave-length for each element. The dis- 

 cussion of all the material thus accmnulated has had to be deferred, 

 but it is planned to use it for a further examination of the correspond- 

 ence between the Zeeman effect and other agencies known to affect the 

 wave-length of spectrum lines. 



STANDARDS OF WAVE-LENGTH. 



A few plates have been taken by Mr. Babcock with the interferometer 

 in connection wdth the 13-foot Littrow spectrograph for the determina- 

 tion of wave-lengths of carbon and calcium lines in terms of the iron 

 secondaries. The values obtained are in excellent agreement with 

 those made by means of the grating. 



Of the 32 photographs with the new interferometer apparatus now 

 availal)le, a few have no measurable exposures on the red cadmium line, 

 but about one-half have been measured and reduced. The 5, 7.5, 

 10, and 15 mm. etalons have been used, the first for a majority 

 of the plates. In the region XX 4100-5050 about 150 iron lines have 

 been measured in terms of the red cadmium line, but the final 

 wave-lengths await the evaluation of small corrections still to be 

 applied. The method finally adopted for the reduction of the plates 

 involves the measurement of the linear diameters of five rings for each 

 line and the calculation of the fractional order of interference by a 

 simple least-squares solution of the observational equations, which 

 is carried out very rapidly. The uncertainty in a single detennination 

 of the order of interference found in this way for good lines is about one 

 part in four or five millions, /. c, about 0.001 A in the wave-length. 

 The method entirely avoids the measurement of focal lengths of lenses 

 or mirrors. 



