144 Professor BapTiael Meldola on the Photographic Image. [May 16, 



they lack that definiteness which the modern chemist regards as the 

 essential criterion of chemical individuality. The investigation 

 may lead to the recognition of a new order of chemical attraction, 

 or of the old chemical attraction in a different degree. The 

 chemist who discourses here ujDon this subject at the end of the 

 half-century of photograj^hy into which we have now entered, will 

 no doubt know more about this aspect of chemical affinity ; and if 

 I may invoke the spirit of prophecy in concluding, I should say that 

 a study of the photographic tilm with its invisible image will have 

 contributed materially to its advancement. 



[K. M.] 



