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Physics. — "Clumgc of inavi'lriujlh of the middle line of triplets.'' 

 (Second Part). By Prof. P. Zkkman. 



6. We will now return to the observations of § 4. Arranging these 

 according to strength of field it appears that the distance a' — a!' changes 

 considerably with increasing magnetic intensity. The displacement 

 of line 5791 is not a linear function of the strength of the lield but 

 increases more rapidly than would folhnv from this simple I'elation. 

 However it is impossible without further consideration to deduce 

 the law of displacement, because, as remarked in § 4, the distance 

 of the lines of comparison does not remain invariable. This is the 

 reason why somewhat different values of a' — a" are obtained, when 

 these are calculated from the change of a—a', than when the change 

 of b -a' is considered. 



The direction however of the displacement of 5791 is easily 

 determined. It is towards the red end of the spectrum. A shift 

 towards the side of increasing wavelengths corresponds in the figure 

 of § 3 to a displacement in the direction from a towards a" . The less 

 refrangible side of line 5791 is easily distiuguished upon the negatives 

 by the observation of the two weak less i-efrangible companion lines 

 and the one weak more refrangible companion line ^). 



7. The shift of the middle line of the triplet may be demonstrated 

 also by our method of the non-uniform field, if an echelon-spectroscope 

 is made use of. A curvature of the middle line will be the immediate 

 effect of the shift. If we use Rowland's grating such a curvature 

 would be invisible nor have I observed it in that case. 



The visibility of the curvature will be much increased by taking 

 care that in the image points corresponding to very different intensities 

 of field lie closely together. In order to attain this an eleven times 

 reduced image of the vacuum tube, charged with mercury and placed 

 into the field, was projected on the slit of the auxiliary spectroscope. 

 The lens used was a photographic objective of 10 cm. focus. 



The Plate gives somewhat enlarged reproductions of negatives 

 I'clating to line 5791 resp. Hue 5770. The middle line is given in 

 two succeeding orders. Between these the other components of the 

 triplets are seen. With increasing magnetic force the components 

 deviate further and further from their own middle line. In the 

 central pai't of the field of view the maximum distance is reached. 



1) Janicki. Feinere Zerleguiig dor Spektralliuieu von Quecksilber u.s.w. hiaugural, 

 Diss. Halle a. S. 1905, Annalen der Physik. Bd. 19, 36. 1906. 



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