CONTEMPORARY ADVANCES IN PHYSICS 



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carbon tetrachloride, the triad of Hnes to the right of 4358, and the 

 equally- spaced triad to its left. These latter are "anti-Stokesian" 

 lines — I will presently explain the name — and consist of quanta which 

 have received as much energy from molecules as the quanta of lowered 

 frequencies have given up. With carbon tetrachloride they are extra- 

 ordinarily bright. Notice again how these lines and the hazy doublet 

 still further out are repeated to the right of 4046, where they are in- 

 terspersed with other lines which are primary lines unshifted; and 

 again on both sides of 5461. 



Fig. 6 — Ultraviolet light scattered by sulphuric acid; at the right, 2536 accompanied 

 by numerous shifted lines. (R. M. Langer.) 



In Fig. 6 we pass to another region of the spectrum, the ultra violet. 

 On the extreme right is the strong line 2536 of the mercury spectrum, 

 scattered unshifted by sulphuric acid ; the numerous lines beside it are 

 Raman lines. 



In Fig. 7 the scattering substance is water; the novel feature of the 

 scattered light is a set of diffuse bands, each shifted from a certain 

 line of the primary spectrum. It is frequently observed that the 

 shifted lines, and the unshifted lines as well, are broader and hazier 

 than those of the primary light, an effect attributed to conversion of 

 the energy of the quanta into energy of rotation of the molecules. 

 Water however shows a quite remarkable broadening, if this be the 



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Fig. 7 — Light scattered by water; note the diffuse bands shifted from the sharp lines. 



(R. M. Langer.) 



way to describe it; it has been attributed to association of molecules. 

 A few special words must be said about the shifted lines which are of 

 higher frequency than the primary light responsible for them — not 

 because they are really more remarkable than the others, but because 

 somehow they seem less to be expected. They are called by the 

 monstrous name "anti-Stokesian" because in fluorescence such lines 

 run counter to a principle laid down by Stokes; it seems cruel to per- 

 petuate a mistake in this way. They consist of quanta which have 

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