176 REPORTS OF INVESTIGATIONS AND PROJECTS. 



In the investigation of the Zeeman effect by Dr. King, magnetic fields rang- 

 ing from 12,000 to 20,000 gausses were employed. High dispersion photo- 

 graphs of the spectra were made by means of the large grating spectrograph. 

 Suitable adjustments of the magnet and optical system then gave means of 

 producing numerous modifications in the resolution of the spectral lines, so 

 that as a rule a close duplication could be obtained of the character of the 

 separation in sun-spot lines. The kind of separation of the lines for light 

 polarized in planes at right angles, the so-called "longitudinal" and "trans- 

 verse" effects, was found to be highly important in this study, as the light 

 from sun-spots corresponds to a mixture of these polarizations. The double 

 lines in spot-spectra were thus found to be quadruple in the laboratory, the 

 absence of a central component permitting the relatively weak solar magnetic 

 field to show the doublet separation. There is also a close correspondence 

 between the lines appearing triple in the spectra of sun-spots and in the lab- 

 oratory. 



The main branches of the Zeeman work have been as follows: (a) the 

 measurement of the separations of components of lines in the spectra of iron, 

 chromium, titanium, and nickel, for the comparison of the magnitude of 

 separation and testing of Preston's Law; (b) determination of the plane of 

 polarization of the light producing the several components of each line ; thus 

 for a quintuple line it is necessary to know whether the outer pair of com- 

 ponents is produced by light vibrating parallel or perpendicular to the lines 

 of magnetic force; (c) the variation in relative intensity of components 

 polarized in different planes, produced by changing either the direction of the 

 field or the arrangement of the observing apparatus; (d) the production of 

 asymmetry in the intensity of components of separated lines by special ex- 

 perimental conditions which exist to a greater or less extent in the tower tele- 

 scope; (e) the comparison of the Zeeman effect for absorption and emission 

 spectra. 



The large electric furnace has been used by Dr. King for an intensive study 

 of the spectra of iron, chromium, titanium, vanadium, manganese, calcium, 

 nickel, and cobalt, preliminary results of which were reported last year. 

 These spectra, most of them having many lines, have been photographed 

 under sufficiently high dispersion to permit an accurate study of the change in 

 character and relative intensity of the lines as the temperature was raised 

 from the point needed to vaporize the substance up to about 3,000° C. The 

 range of spectrum observed was usually from X 4000 to A 6600. The purpose 

 of the investigation has been not only the production of spectra by means in 

 which temperature is the energizing agency and the comparison with spectra 

 from other sources, such as the flame, arc, and spark, but also a study of the 

 rate of increase in the intensity of lines as the temperature rises. Some lines 

 are found to appear at low temperatures and change but slowly as the tern- 



