F - 



U 



THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



APRIL 1913. 



XLV. The Selective Dispersion of Mercury Vapour at the 2536 

 Absorption Line. By R. W. Wood, Professor of Experi- 

 mental Physics, Johns Hopkins University, and Adams 

 Research Fellow of Columbia University *. 



[Plate III.] 



UP to the present time no quantitative determinations have 

 been made of the selective dispersion of non-luminous 

 absorbing gases. About ten years ago I made a somewhat 

 detailed study of the dispersion of sodium vapour, and a good 

 deal of work has been done since by other observers, working 

 along similar lines, but in the case of this vapour no one has 

 succeeded in working under conditions of known density, 

 for the vapour cannot be bounded by transparent solid sur- 

 faces on account of the chemical action which it exerts. 

 Ladenburg and Loria's determinations of the dispersion of 

 hydrogen at the a and ft lines are not open to this objection, 

 but in this case the absorption and dispersion results from 

 the circumstance that the gas is ionized and rendered luminous 

 by the electric discharge, and the conditions are consequently 

 a little more complicated. 



A number of years ago I made some observations of the 

 anomalous or selective dispersion of mercury vapour at the 

 ultra-violet absorption line, the wave-length of which is 2536. 

 This vapour appeared to be an ideal medium for a quantitative 

 investigation of the phenomenon, since it can be contained 

 in transparent vessels of fused quartz, and its vapour density 

 * Communicated by the Author. 



Phil. Mag. S. 6. Vol. 25. No. 148. April 1913. 2 H 



