2$0 ON LIGHT. 



be a movement, or an influence, we must admit in that 

 movement or influence a similar capacity for analysis or 

 composition, or else have recourse to some unknown 

 modification of the one or the other, leaving the phae- 

 nomenon as unexplained as before. There may, for 

 instance, be a great variety of such movements, all 

 luminiferouS) but not all alike ; and some may be de- 

 stroyed, or some exaggerated, in the act of reflexion or 

 transmission. 



(34.) The key to this mystery, up to a certain point, 

 was furnished by Newton, in his analysis of white light 

 by prismatic refraction. A full account of the manner 

 in which that analysis is performed, of the phenomena 

 it presents, and of the nature and subdivisions of the 

 " Prismatic spectrum," is given in our lecture on " The 

 Sun," 29, to which, to avoid repetition, we refer our 

 readers. Let us, however, consider what kind of general 

 theoretical interpretation we are entitled to put on this 

 analysis. Now, the first and most obvious conclusion is, 

 that the phenomenon we have to deal with, is not what 

 in the accuracy of modern scientific language is under- 

 stood by the term " analysis." It is the separation and 

 redistribution (according to degrees of a certain quality 

 common to all its elements viz., that of REFRANGI- 

 BILITY) of a mixture, rather than the dialysis of a . true 

 compound. The simile by which we there illustrated it 

 is so far exact. A glacier moraine might be redistributed 

 by tidal action over the floor of the Ocean ; the great 

 blocks left in situ, or little moved the smaller forming 

 shingle, gravel beds, sandstones, or incoherent muddy 



