426 



Magneto- Optics of Sodium Vapour. 

 Red Rotation Spectrum. 



3 



6218-94 



2 



642745 



5 



623059 



7 



6434-23 



7 



6-235-96 



2 



6435-05 



3 



6240-19 



3 



6438-30 



5 



6252-18 



3 



6441-62 



7 



6255-13 



3 



6445-24 



o 



6260-32 



10 



6449-86 



10 



6262-55 



1 



6470-58 



6 



6272-78 



10 



6481-89 



3 



6283-40 



10 



649036 



3 



6283-84 



7 



6501-45 



10 



6314-14 



3 



6515-69 



6 



6317-09 



4 



6545-91 



10 



6323-81 



3 



6555-71 



2 



6358-65 



5 



6556-66 



10 



6374-11 



7 



6579-55 



4 



637924 



8 



6609-80 



10 



6386-50 



7 



6623-96 



6 



6399-79 



3 



6676-88 



3 



640584 



4 



6692-60 



8 



6419-69 



4 



6745-61 



3 



6i26-85 



5 



6761-19 



:at( 



>ry effects 



of the 



vapour 



8 6005 26 



8 6019-22 



4 6023-45 



5 6027 47 



7 6031-79 

 4 6060 25 



6 606391 



7 6067-47 

 2 6075-42 



10 6107-73 



9 6108-25 

 4 611359 

 2 6113-81 



10 6125-67 



10 6139-17 



8 6162-74 

 2 6166-10 

 6 6172-32 

 4 6179 92 



8 6183-93 



9 6196-93 

 8 6216-56 



The fact that the rotatory effects of the vapour only 

 manifest themselves in a vacuum is of fundamental import- 

 ance. The exact nature of the changes which occur when 

 an inert gas is admitted have not as yet heen determined. 

 The fact that no trace of the red or green rotation spectrum 

 could be seen when the vapour was formed in an atmosphere of 

 hydrogen at atmospheric pressure, and that only a very slight 

 restoration of light was visible at the D lines, led me to infer 

 that the rotatory power had been destroyed. On experi- 

 menting vvith helium light, however, it was found that the 

 rotation measured in degrees was the same after the ad- 

 mission of the hydrogen as before, the intensity of the trans- 

 mitted light being however very much less. On this account 

 it seems probable that the effect of the chemically inert gas 

 is to modify the absorbing power of the gas. It has been 

 found that the presence of hydrogen or nitrogen interferes in 

 a very marked degree with the fluorescence of the vapour. 



The same thing is true in the case of iodine vapour, which 

 has been found to possess a very great rotatory power for 

 green light, when the vapour is formed in an exhausted tube. 

 A small bulb, containing a few crystals of iodine, is exhausted 

 and sealed off from the pump. On placing it between the 

 poles of the magnet between crossed nicols, a most beautiful 

 emerald-green light is restored the moment the current is 

 turned into the coils. The spectrum of this light has been 

 photographed and observed visually. It resembles the ab- 

 sorption spectrum so closely as to lead to the belief that the 

 narrow black lines in it are produced by absorption. Little 



