lines of neon, helium and sodium in a magnetic field. 49 



the author with the Rowland grating. To accomplish this, a 

 copper slide was attached to the slit of the spectroscope, and slotted 

 in such a way that, in one position, the upper half of the image was ' 

 cut off during the normal vibrations of the gas, and, in another 

 position, the lower half was cut off when the vibrations were under 

 the influence of the magnetic field. No other alteration was made ; 

 the position of the photographic plate was not altered ; the neon 

 tube was not touched; and the discharge through the gas was 

 exactly the same in both series of experiments. The two images 

 were consequently photographed directly over each other ; and the 

 following table contains the numbers, in thousandths of an 



Angstrom unit, of the shift towards the red end of the spectrum 

 of the middle constituent of the triplets, as well as of the shift 

 observed in the sextet from 6383'15, produced by a field of 

 24,000 units. 



The + sign meaning, as before, that the shift is in the direc- 

 tion of greater wave lengths. 



Efforts were also made to measure the shifts of some of the 

 lines which give more than three constituents. For example, 

 Lohmann states that the line 6096 is divided into nine con- 

 stituents. On my plates, there are three diffuse constituents, 

 and there are doubtful signs of further subdivisions; but the 

 latter are not sufficiently well marked, so that the measurements 

 were made from the centre of the middle diffuse constituent. 

 The same remark applies to 6678 and 6506 which are stated by 

 Lohmann to divide into nine constituents, and to 6402 which 

 is stated to divide into 15 constituents. There is no doubt that 

 there is a shift of these lines towards the red end of the spectrum 

 when tihey are vibrating in the magnetic field, but for the reason 

 just stated, the measurements are not of the same degree of 

 certainty as those obtained from the above triplets. 



X 



6678 

 6506 

 6402 

 6096 



Shift in thousandths of an A.U. 

 + 90 

 + 80 

 + 45 

 + 74 



The numbers indicate that the shift is different for different 



VOL. XV. PT. I. 



