

Scattering and Regular Reflexion of Light. 329 



between the extreme components of the 4388 line was 

 15*7 A.U., and, according to Stark's measurements in the 

 case of an electric field of 28,500 volts, per cm., this separation 

 would correspond to a field-strength of about 37,000 volts 

 per cm. The 4686 line showed a definite broadening in the 

 dark space, but no definite components could be identified. 

 The line in the strongest photographs appeared to be 

 broadened nearly symmetrically, and the intensity of the 

 outside edges was less than the middle portion of the line. 

 The total width of the line in the dark space was about 

 3' 7 A.U., and the corresponding distance between tho 

 components of H^ was 7*2 A. (J. Each of the components of 

 Hp was double, but the lines were too diffuse for an accurate 

 estimate of the distance between the outside components. 

 However, by making use of Stark's results, it could be 

 calculated that this distance was approximately 10 A.U. 

 For the sake of comparison the widths of the 4686 and Hp 

 lines were measured in the region above the dark space, and 

 found to be in each case about 1*4 A.U. Although it is 

 impossible from these results to test quantitatively the simple 

 theory of the Stark effect for the 4686 spectrum line, it 

 seems evident that if the broadening of the line is altogether 

 due to the electric field its magnitude is decidedly less than 

 one-half that of H^. It also follows that it is difficult to 

 explain by means of the Stark effect the great width of the 

 line in comparison with the hydrogen lines when they are 

 generated by a condenser-discharge. 



University of Manchester, 

 July 1916. 



XXXVII. Scattering and Regular Reflexion of Light by an 

 Absorbing Gas. By H. W. Wood and M. Kimura*. 



[Plate VI.] 



IN previous papers f by one of us, it has been shown that 

 mercury vapour, at room temperature, in an exhausted 

 quartz bulb, when illuminated by the light of a quartz 

 mercury arc, re-emits diffusively a monochromatic radiation 

 of wave-length 2536, which has been named resonance 



* Communicated by the Authors. 



t R. W. Wood, " Selective Scattering and Absorption by Resonating 

 Gas Molecules," Phil. Mag. May 1912. 



Phil. Mag, S. 6. Vol. 32. No. 189. Sept. 1916. Z 





