On the Polarized State of the Gas in a Crookes’s Layer. 119 
which is red hot, and the other below the temperature of boiling 
water, and with an interval between them of a quarter ofa 
millimetre, then one-fiftieth of the light will be restored in an 
analyzer which was so turned as to extinguish the beam before 
transmission between the plates. Such an effect could be easily 
observed, but asit is very unlikely that the whole of the strain 
in a Crookes’s Layer is due to a difference of density of the gas in 
different directions, itis very unlikely that so great an effect would 
be produced. One object, however, in trying the experiment 
would be to determine to what extent the strain is due to a 
ditterence of densities. 
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