Regular Reflexion of Light by an Absorbing Gas. 343 



The Structure of the 253(J Line. 



The interesting work of Malinowski (Aim. der Pliysik, xliv. 

 p. 947, 1914) has made it appear extremely probable that 

 the 253G line is, in reality, not a single line, but a very close 

 multiple line. On this account we have investigated the 

 structure of the resonance line with a quartz Fabry and 

 Perot interferometer. 



Malinowski found that, if the resonance lamp was placed 

 in a magnetic field, and excited by a lamp outside of the field, 

 the intensity of the resonance radiation increased rapidly with 

 an increase of field strength, reaching a maximum at 1000 

 gauss, and then passing through successive minima and 

 maxima. 



The first maximum is easily explained as follows : — 



Assuming the 2536 line of the exciting lamp to be more or 

 less reversed, as is sure to be the case with a lamp of the 

 ordinary type, it is clear that the magnetic components of 

 the resonating vapour in the magnetic field will respond to 

 the frequencies to the right and left of the centre of the 

 reversed line where the intensity is greater. 



The fact that successive maxima and minima occur indicates 

 that we are not dealing with a single line, and a normal 

 Zeeman effect. Malinowski obtained a curve of similar type 

 by placing the resonance lamp in a magnetic field and passing 

 its radiation through a quartz cell containing mercury vapour 



at room temperature. As ordinates he took the ratio -j-, in 



. 

 which J is tlie intensity after passage through the absorption 



cell, and J the intensity (for a given field) without the cell. 



This compensates for the variations of J with the field, and 



the curve shows the transmitting power of unmagnetized 



mercury vapour for the resonance radiation of mercuiy 



vapour in a field, of varying strength. A similar curve was 



also obtained when the absorption cell was placed in the 



magnetic field and the resonance lamp outside of the field. 



These results indicated that the absorption line and emission 

 (resonance) line had a similar complicated structure, and 

 behaved in a similar manner in a magnetic field. 



Malinowski showed also that the secondary resonance 

 radiation, excited in a bulb outside of the field by the light 

 of a resonance lamp in the field, gave a curve, the maxima 

 of which occupied the positions of the minima of the curve 

 obtained with the absorption cell, showing that the energy, 

 which was refused passage by the cell, was re-emitted. It 

 was not possible to draw any very definite conclusions 



