TYPES OF SEPARATION. 45 



it being a quintuplet with three n- and two /)-coniponents, the central -component being strongest. 

 Reese (12) made the same error concerning both this line and X 3643.469, together with another farther 

 to the vdolet. Kent (13) followed with a publication in which the lines are correctly described. Cotton (i-O 

 calls attention to the confusion which has come about and gives the correct structure. Runge (2/') cites 

 the first paper of Becquerel and Deslandres and that of Reese concerning the inverted triplet, without 

 noting that the error had been corrected in each case by later publications, though Runge later (2<r) repro- 

 duced the diagram of Becquerel and Deslandres from their second paper, in which the correct structure 

 of these lines is given. Other works on spectroscopy speak of the inverted triplet, the basis for this 

 being the publications which have been mentioned. No real case of the inverted triplet has presented 

 itself in the iron or titanium spectrum, nor, so far as the author is aware, does such a type exist in any other 

 spectrum. Apparent examples of such inversion are hkely to appear on plates not fully exposed, since 

 some quintuplets, X4464.6i7 of titanium for example, show a central M-component very much stronger 

 than the two outer ones, so that the central component may easily appear alone. 



The tendency of Zeeman components to follow the appearance of the no-field line as regards sharp- 

 ness or diffuseness frequently makes it difficult to judge whether a line is a true triplet or not. If the 

 lack of sharpness is not due to the character of the no-field line, a doubtful triplet may be (i) a quadruplet 

 if the difi'use /^-component is really double, (2) a sextuplet if each of the three widened n- and ^-com- 

 ponents are double, (3) a septuplet if the two M-components are double and the /^-component has three 

 close constituents. Still higher separations for doubtful triplets are not impossible, but probably there 

 are very few such. The criterion for distinguishing between these possible types is given on p. 19. 



3. Quadruplets. 



The unquestioned quadruplet is somewhat rare. The great majority of lines having two n- and two 

 /(-components have their w-components widened to some extent and are usually classed as doubtful 

 sextuplets, since so many of these have been resolved by the strongest fields used that it seems probable 

 that a still stronger field would show four ^-components for such lines in every case. Occasionally, how- 

 ever, the two M-components are sharp. The relative separation of n- and /^-components varies greatly 

 for different lines, but the /^-components are almost always closer together. The most decided excep- 

 tion is the titanium line X 4398.460, apparently a quadruplet, whose ^-components show only two-thirds 

 the separation of the p pair. 



4. Quintuplets. 



The quintuplet appears least often of any of the less complex types. As a rule this separation gives 

 three n- and two /J-components, the distance between the /^-components being the same as between the 

 outer w-components. The central ^-component is the strongest of the three, and the effect when the light 

 is observed at right angles to the lines of force without a Nicol prism is to give a triplet, the components 

 of which are of about equal intensity, caused by the superposition of the p doublet on the two outer 

 M-components. Good examples are XX3733.469 and 3865.674 of iron, and 4291. 114 of titanium. The 

 first two were originally mistaken for "inverted triplets" on account of the strong central M-component. 

 Dissymmetry is sometimes present, as in X 5455.834 of iron. A different type is presented in X 4710.368 

 of titanium, which shows four w-components and a single sharp />-component. No similar line has been 

 observed in either of these spectra. 



5. Sextuplets. 



This t>pe usually has the two pairs of -components of equal intensity, shown by a uniform widening 

 in cases where the pairs are blended. As has been previously noted, the sextuplet is a very common 



