150 Mr. Alex. Hodgkinson on 



such instances as I myself possess, and am therefore able 

 to show you. As examples of pigmentary colours, I need 

 only name one or two for the sake of comparison, since the 

 colours of most objects ordinarily met with are pigmentary. 

 Leaves, flowers, dyes, birds, fish, insects, minerals, &c, 

 exhibit these colours, some almost entirely, and all, 

 excepting fish, in far the majority of instances. Of objects 

 displaying iridescent colours we have also examples in the 

 various divisions of the animal, vegetable, and mineral 

 kingdoms. Amongst birds the most striking examples are 

 found amongst the Humming Birds, Sun Birds, Birds of 

 Paradise, &c. Insects, again, furnish numerous examples, 

 more especially amongst tropical species, though not, 

 perhaps, proportionally in greater numbers than amongst 

 those belonging to our own more temperate regions. The 

 colours of fish are almost entirely iridescent, since their 

 very whiteness, or silvery sheen, is due to the admixture of 

 the iridescent colours of innumerable minute thin lamellre, 

 too small to be seen individually with the naked eye, but 

 plainly perceptible under the microscope. In the Vegetable 

 kingdom iridescent colours are far more numerous than is 

 ordinarily recognized, since the surfaces of the cell walls 

 produce interference colours which are more or less obscured 

 by the pigmentary colours of leaves and coloured flowers, 

 but may be readily seen in the case of white flowers by the 

 aid of a lens and sunlight. Under these conditions each cell 

 may be seen to sparkle with its own iridescent colour, 

 forming, by admixture of the interference tints of neigh- 

 bouring cells, the varying shades of white seen in numerous 

 flowers which are devoid of pigmentary colour. Mineral 

 bodies displaying iridescent colours are also numerous ; 

 opals, sunstone, fire-marble, felspar, mica films, tarnish on 

 various metallic crystals, certain crystals of chlorate of 

 potash, &c, are examples. 



In describing the various natural objects for purposes of 



