CORRELATION OF PHENOMENA 65 



the hope of arriving, sooner or later, at some 

 consistent explanation — for there would be little 

 doubt that such an explanation does exist — of these 

 manifold, and indeed in some cases apparently 

 mysterious phenomena. 



Fluorescence and phosphorescence are, to our mind, 

 connected with all these, whilst the class of effects 

 almost invariably associated with them, being of a 

 more persistent type than other modes of luminosity, 

 form in many instances a more powerful, and in most 

 cases a more tangible, means of research. 



It is, therefore, a definite object which should 

 be kept in view in such matters, that of reaching, if 

 it can be reached, a comprehensive dynamical theory, 

 and commencing with the construction of mechanical 

 models, to illustrate the principles involved in the 

 facts, although, as we shall find, such facts do not 

 always admit of simple dynamical representation, 

 except by the stepping-stones, as it were, of a mole- 

 cular theory, before such mechanical analogies as we 

 may hope to arrive at can be constructed. 



Luminosity, which to the ancients, like Hippo- 

 crates, was a form of life, is to us a manifestation, 

 however modified, of the simplest forms of meta- 

 bolism, of, we may say, a continual and continuous 

 change, of the building up and breaking down of 

 complex molecular agglomerations, although of a far 

 simpler kind than those which in a similar manner 

 constitute the vital processes of the organic world. 

 Here, however, we come within the realm of analogy 

 rather than that of hypothesis. But, whatever we 



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