32 



explained M by Mr Cotton himself, all signs of gp must there be 

 reversed. 



In the folhjwing table a summary is given of the qualitative 

 results of Mr Cotton's experiments. [In all easet? below marked * 

 the direction of revolution is stated for wave-lengths adjoining Zq. 

 For wave-lengths much greater or much less than /q the direction 

 of revolution is sometimes the reverse of that here indicated. This 

 is indeed what might have been expected. We must remember that 

 in forming equation (1) of Art. 4 we have ignored all other except 

 the Aq- vibration; and it is clear that we should not be justified ia 

 assuming that the /l^- vibration can control exclusively the beha- 

 viour of a given substance beyond a certain distance in the spectrum]. 



I. Solution uf dextrogyric copper tartarate in caustic potasb 

 {Th^se, pp. 58— 60 1 ; Z < A^. 



Observed rotation : <j^ . ip^^O 



Observed revolution: left-handed. 



II. Solution of laevogyric copper tartarate in caustic potash' 

 {lliese, p. 58 j; X < /o- 



Observed rotation : ^ <C , </> > 

 Observed revolution: right-handed. 



III. Solution of dextrogyric copper tartarate in caustic soda 

 {Thlse, p. 63 1 : ;.<:/o. 



Observed rotation : ^ XJ . t^ <C 

 Observed revolution: left-handed. 



IV. Solution of double chromium and potassium tartarate (2A^e,, 

 pp. 65 — 67), 



a) / > /o b) / <: >io 



Observed rotation: qX). tp <Z0 ^<;0. tp>0 

 Observed revolution: right-handed * riofht-handed * 



V. Mixture of potassium tartarate and chromium alum solution 



{Th^e, p. 71). 



SL) I > /o b) X<iXf^ 



Observed rotation : o>0, ^"^O ()<;0, ^>0 



Observed revolution: right-handed * right-handed * 



') Journal de Pfit/sique thdoriqtie et appliqude, III Serie. tome VII, p. 84, 

 Paris 1898. 



