VARIOUS OPINIONS. 



Sir David thought that the experiments required to be 

 repeated by persons acquainted with those branches of 

 physical optics with which the phenomena were inti- 

 mately allied. It is very easy to explain why a fish 

 may appear dark in a dark vessel, and light in a 

 coloured one ; and why it should have a still different 

 appearance when taken out of both vessels and exposed 

 to the light of the sun. All bodies assume the colour 

 of the light which they reflect, and a brilliant light will 

 develop colours which are invisible in light of ordinary 

 intensity. As the peculiar colours of fishes depend on 

 the thickness or size of certain minute transparent 

 particles, it is not easy to understand how the fish 

 could voluntarily alter the size or thickness of those 

 particles, or how exposure to another colour could 

 permanently produce the same mechanical effect. If 

 a fish is kept in mossy or muddy water, it will doubt- 

 less absorb the colouring matter which the water may 

 contain ; but this is rather a process of dyeing than 

 one of physiological action. The changes said to take 

 place in the colour of fishes when dying might arise 

 from the drying of their scales, which produces a 

 change in all colours, but particularly in those of thin 

 films, which are quite different when they are dry 

 from what they are when immersed in a fluid. 



" A conversational discussion then took place, in 

 which Professor Connell supported Dr. Gillespie's 

 views, and Dr. Reid those of Sir D. Brewster." 



This subject is in such good hands, that I shall not 

 intrude any speculative observations of my own. "VVe 

 have lately seen such wonderful effects produced by 



