The Nature Column.

Digger (Invercargill RSA), Issue 24, 27 August 1920, Page 6

The Nature Column.

(By "Student.")

("Student" will be pleased to reccive notes on any branch of Natural History. Observations on birds, insects, plants, etc., will be equally welcome. If using a pen-name, will correspondents please enelose real name and address.) The other day in Elles Road I saw a beautiful chaffinch with shining blue green head. It was so beautifully coloured that for the moment I thought it must be some other bird. I am told that exceptiomwly well-coloured cockbirds are occasionally seen. In many uirds the blue and green colours are largeiy an effect of the diffusion of light and are not altogether due to pigments. The sky is blue hecause the water in the air has a selective action dipersing blue light and absorbing the red. The red light of the sunset is caused by sun-.'ight transmitted through the clouds. A hotile of mineral oil has a beautiful blue colour by reflected light but is r,ed or yellow when viewed by transmitted light. The blue of the sea., lakes, etc,., is caused by reflected light from the bottom and from particles floating in the water. If the bottom is a-t a grea-t depth, the water may appear hlack as it does in sorne of our cold lakes. The eyes of a baby are blue from similar causes. Later on a yelow pigment appears in the eye and this in combination with the structural blue causes the range of colours through blue and green to dark brown. This is not strictly true for white pigment is foraM on a butterfly's wing and on the underside of fish. Latest investigations go to show that the colours of a butterfly's wing are on the surface and the colours would be different if viewed with transmitted light. The majority of white markin.gs are caused by minute air bubbles. The whiteness M the liiy and other flowers is so caused. Grey hair arises in the same way and not through absence of pigment, though why grey hair should come so swiftly as it sometimes does, is not yet known. Another familiar instance of a white being produced from a eolourness subso.Mice is the froth on the aeashore. The blues and gmeens in birds are (heret'or.e most likely caused by the same means as the blue of the sky. The substance of a feather includes innumerahle air bubbles and these in conjunction with a dark pigment, usually brown, giverise to the blue colours. Yh,e brown pigment obsorbs the red. A yellow pigment gives in conjunction with the structural blue a green colouration. If the yellow pigment is in sufficient quantity the result will be a yellow bird. The bright red colours of the Flamingo were at one time attributed to its diet. It has now been established that the diet doeg not affect the colour. It is supposed that the red colour is caused by oil on the feathers through which light is transmitted. Anything approaclring a blue feather has as yet not been made in the laboratory. Some frogs are of a brilliant blue colour owing to the absence of pigment, and an Australian green tree frog was mis-named the sky blue frog owing to the specimen liaving ibeen preserved in spirits and thus lost its yellow pigment. If fhe veliow pigment be scraped off this frog it becomes quite blue. A simple experiment easily performed is to take a crystal of biuestone (copper sulphate) and crush it to a fine powder. The beautiful blue is lost. Other cystalline substances exhibit the same features. Before leaving the subject it shmM be remembered that light can penetrate some metals. For instance the colour oi gotd is green wlien beaten out very thin and viewed by transmitted light. The light reflected from several surfaces of silver is yellow. When the metals are precipitated as fine powder, they are in many cases of a totally different colour. In the near future it is expected that rouge will be ground so fine that it will become yellow. In ' conclusion it may be added that, the peeuliar metallic sheen seen on some birds is probably dne to the presence of a pigment which act-s like analine colours. Orystals of these last-named viewed by reflected light look metallic though by transmitted light they are red or some other colour. The researcfi now being carried on in respect to the effects of light in the colouration of insects, etc, may soon g.ve us inforination as to the way in which protective colouration is develped.