394 



Secondly, the action of the spectrum is confined, or nearly so, to 

 the region of it occupied by the luminous rays, as contra-distinguished 

 both from the so-called chemical rays beyond the violet, (which act 

 -with chief energy on argentine compounds, but are here for the 

 most part ineffective,) on the one hand, and on the other, from the 

 thermic rays beyond the red, which appear to be totally ineffective. 

 Indeed, the author has not hitherto met with any instance of the 

 extension of this description of photographic action on vegetable 

 colours beyond, or even quite up to the extreme red. 



Besides these, the author also observed that the rays which are 

 effective in destroying a given tint, are, in a great many cEises, those 

 w^hose union produces a colour complementary to the tint destroyed, 

 or at least one belonging to that class of colours to which such com- 

 plementary tint may be referred. Yellows tending towards orange, 

 for example, are destroyed with more energy by the blue rays ; blues 

 by the red, orange and yellow rays ; purples and pinks by yellow 

 and green rays. These phenomena may be regarded as separating 

 the luminous rays by a broadly defined line of chemical distinction 

 from the non-luminous ; but whether they act as .such, or in virtue 

 of some peculiar chemical quality of the heat which accompanies 

 them as heat, is a point which the author considers his experiments 

 on guaiacum as leaving rather equivocal. In the latter alternative, 

 he observes, chemists must henceforward recognise, in heat from 

 different sources, diffierences not simply of intensity, but also of 

 quality ; that is to say, not merely as regards the strictly chemical 

 changes it is capable of effecting in ingredients subjected to its in- 

 fluence. 



One of the most remarkable results of this inquiiy has been the 

 discovery of a process, circumstantially described by the author, by 

 which paper washed over with a solution of ammonio-citrate of iron, 

 dried, and then washed over with a solution of ferro-sesquicyanuret 

 of potassium, is rendered capable of receiving with great rapidity a 

 photographic image, which, from being originally faint and some- 

 times scarcely perceptible, is immediately called forth on being 

 washed over with a neutral solution of gold. The picture does not 

 at once acquire its full intensity, but darkens with great rapidity up 

 to a certain point, when the resulting photograph attains a sharpness 

 and perfection of detail which nothing can sui^Dass. To this pro- 

 cess the author applies the name of Chrysotype, to recall to mind its 

 analogy with the Calotype process of Mr. Talbot, to which in its 

 general effect it affords so close a parallel. 



2. " Experimental Researches on the Elliptic Polarization of 

 Light." By the Rev. Baden Powell, M.A., F.R.S., Savilian Pro- 

 fessor of Geometry in the University of Oxford. 



This paper contains an experimental investigation of the pheno- 

 mena of elliptic polarization resulting from the reflexion of polarized 

 ligjht from metallic surfaces, and the theory on which they are ex- 

 plicable ; the analytical results being given in a tabular form, and 

 applied to the cases of the experiments themselves. 



