THEORY AND FORMER INVESTIGATIONS. 7 



base this conclusion. The refusal of banded spectra, notably that of carbon, to show either Zeeman effect 

 or displacement has often been cited as probably resulting from a connection between the two phenom- 

 ena, and interesting developments on this point have recently been presented. Dufour (45) obtained 

 Zeeman separations for the component lines of the band spectra of the chlorides and fluorides of the 

 alkaline earths, the magnitude of separation being about the same as for line spectra. A short time 

 after, Rossi 146) selected three of these, the fluorides of calcium, strontium, and barium, and obtained 

 distinct pressure shifts for the bands, the shift being of the same order as for line spectra. Comparing 

 his results with those of Dufour, Rossi did not find any general relation between the magnitude of 

 the two effects. Numerous investigations on the Zeeman effect for banded spectra have been made 

 during the past two years, part of which are summarized by Dufour (47), but corresponding results 

 for pressure have not been obtained. 



A detailed comparison of Zeeman separation and pressure displacement for the line spectra of iron 

 and titanium will be made in the present paper. 



3. Former Investigations of the Zeeman Effect for Iron. 



Passing to special investigations on the iron spectrum in which the magnetic separations for certain 

 lines have been described and measured, the first to be mentioned is that of Becquerel and Deslandres (9). 

 In this, 10 lines are given from X3821 to X3873, most of them of complex separation. Shortly after, 

 these writers used a stronger field and covered a larger region. This pubhcation (10) gives no measure- 

 ments, being confined to a description of a few interesting t^pes of lines. 



A note by Ames, Earhart, and Reese (n) speaks of the general characteristics of the iron lines between 

 X3500 and X4400, with special mention of the type of separation for a few lines. Reese (n) gives measure- 

 ments of the separation for 23 of the stronger lines in this region, the source being a carbon spark with 

 iron as an impurity. Kent (13) continued the investigation with better equipment, measuring about 90 

 iron lines between X 3550 and X 4550. Special attention was paid to a number of complex lines. Reese 

 had observed that the fines on his plates could be classified as to amount of separation in about the same 

 way that they were classified as to pressure displacement. Kent, with more material available for com- 

 parison, found that this relation was not verified. 



The paper by Zeeman (30) was concerned chiefly with the question of a dissymmetry of the side compo- 

 nents of triplets, as measured from the central line. Hartmann (48) investigated the structure of a num- 

 ber of iron fines with the echelon spectroscope. He did not, however, obtain as good resolution of com- 

 plex tj-pes as was given by the grating method in the present investigation. The most extensive set of 

 measurements thus far pubfished on the iron spectrum is given in the thesis of Mrs. van Bilderbeek (49). 

 These are from photographs made with a concave grating for a magnetic field of 32,040 gausses. Measure- 

 ments are given for 137 fines between X 2382 andX4529. Of these fines 55 (40 per cent) are to the violet 

 of the region covered by my photographs; the others are the stronger fines among those given in my 

 tables, and have been of great service in determirung the field-strength. As will be noted later, there is 

 an excellent agreement between the two sets of measures for all fines whose components are sharp enough 

 to give measurements of high weight. Besides checking my standard field, the agreement between Mrs. 

 van Bilderbeek's field-value and that which I had obtained by other methods supports the contention 

 in her paper that the field-strengths pubfished by Kent and by Hartmann are both low. 



It wiU thus be seen that several investigations of special regions have been carried out for the iron 

 spectrum with regard to the Zeeman effect. The region covered, however, has not extended beyond 

 about X 4500, with the exception of a few lines in the green examined by Hartmann, lea\'ing nearly three- 

 fourths of the range included in this paper as new territory. For the region from X3700 to X4500, which 

 has been covered to some extent by others, the previous investigators have measured only the stronger 

 fines, the description of the character of separation is usually brief or lacking, and the complex separa- 



