VARIOUS OPINIONS 59 



be repeated by persons acquainted with those 

 branches of physical optics with which the pheno- 

 mena were intimately 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 thick- 

 ness 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 

 doubtless 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. We have lately seen such wonderful effects 



