Coloration 



SCIENTIFIC SIDE-LIGHTS 



108 



green, and the green sifts it by quenching 

 the red, both exhibiting the residual color. 

 The process through which natural bodies 

 acquire their colors is therefore a negative 

 one. The colors are produced by subtrac- 

 tion, not by addition. This red glass is red 

 because it destroys all the more refrangible 

 rays of the spectrum. This blue liquid is 

 blue because it destroys all the less refran- 

 gible rays. Both together are opaque be- 

 cause the light transmitted by the one is 

 quenched by the other. In this way, by the 

 union of two transparent substances we ob- 

 tain a combination as dark as pitch to solar 

 light. This other liquid, finally, is purple 

 because it destroys the green and the yellow, 

 and allows the terminal colors of the spec- 

 trum to pass unimpeded. From the blend- 

 ing of the blue and the red this gorgeous 

 purple is produced. TYNDALL Lectures on 

 Light, led. 1, p. 32. (A., 1898.) 



534. COLOR A PROTECTION Bird 



Feeding on Ground Tree-trunk a Hiding- 

 place. The Sclerurus, altho an inhabitant 

 of the darkest forest, and provided with 

 sharply curved claws, never seeks its food 

 on trees, but exclusively on the ground, 

 among the decaying fallen leaves; but, 

 strangely enough, \vhen alarmed ,it flies to 

 the trunk of the nearest tree, to which it 

 clings in a vertical position, and, remaining 

 silent and motionless, escapes observation 

 by means of its dark protective color. HUD- 

 SON Naturalist in La Plata, ch. 18, p. 240. 

 (C. &H., 1895.) 



535. COLOR AS PROTECTIVE FROM 

 HEAT White for Military Uniforms. By 

 instinct, or perhaps as the result of the ex- 

 perience of centuries, the native Algerians 

 have adopted white as the color for their 

 clothing. Evidently they never dream of 

 manufacturing uniforms of colored woolen 

 cloth. It would be possible to shade sol- 

 diers on a march, or other expedition, from 

 the sun's rays, with the aid of a simple cot- 

 ton burnoose at only a slightly increased 

 cost, and whose volume would be very little. 

 This is an experiment worth trying, at least 

 on a small scale; the use of this vestment 

 would have as an immediate result the pla- 

 cing of the soldier within a medium cooler 

 by ten or a dozen degrees, and all physicians 

 who have accompanied troops on a march 

 are aware that a number of degrees more or 

 less for a man that is fatigued, or has an 

 attack of fever, or is wounded, is a question 

 of life or death. In any case, it would al- 

 ways be well to place some of these white 

 vestures at the disposal of the physician for 

 the use of sick men menaced or attacked by 

 congestion during a march. COULTER Ex- 

 periences sur les Etoffes qui scrvent a con- 

 fectionner les Vetements Militaires, p. 138, 

 Journal de la Physiologic de I'Homme et des 

 Animaux. (Translated for Scientific Side- 

 Jjights.) 



536. COLOR, DEPENDENCE OF, ON 

 OBSERVER Color-blindness The World in 

 Chiaroscuro. It is agreed alike by physi- 

 cists and physiologists that color does not 

 exist as such in the object itself, which has 

 merely the power of reflecting or transmit- 

 ting a certain number of millions of undu- 

 lations in a second, and these only produce 

 that affection of our consciousness which we 

 call color, when they fall upon the retina of 

 the living percipient. And if there be that 

 defect either in the retina or in the appara- 

 tus behind it, which we call " color-blind- 

 ness " or Daltonism, some particular hues 

 cannot be distinguished, or there may even 

 be no power of distinguishing any color 

 whatever. If we were all like Dalton, we 

 should see no difference, except in form, be- 

 tween ripe cherries hanging on a tree and 

 the green leaves around them; if we were 

 all affected with the severest form of color- 

 blindness, the fair face of Nature would be 

 seen by us as in the chiaroscuro of an en- 

 graving of one of Turner's landscapes, not 

 as in the glowing hues of the wondrous pic- 

 ture itself. CARPENTER Nature and Man, p. 

 201. (A., 1889.) 



537. COLOR IN FLOWERS AND 

 FRUITS Beauty Subserves a Purpose. Be- 

 tween fruits and flowers, in the matter of 

 color, there is a close and intimate associa- 

 tion. Every schoolboy who is taught botany 

 knows that flowers are colored to attract 

 insects, while the insects in turn cross- 

 fertilize the plants by carrying the pollen- 

 dust from one flower to another flower of 

 the same species. Color in flowers, then, has 

 a purpose all undreamt of by the older bot- 

 anists. What of fruits? Color here, in the 

 logical sequence of events, must be credited 

 with a purpose also. Let us see what that 

 design may be. When you look at an apple 

 or orange you are struck by the apparently 

 big size of the edible part of the fruit, and 

 by the relatively small size of the seeds. 

 Compared with, say, the fruits of a butter- 

 cup, represented by the collection of little 

 dry green bodies borne on the end of the 

 flower-stalk, the apple, orange, peach, plum, 

 and cherry are grandiose in the extreme. 

 The apple-substance does not nourish the 

 seed. There is no question of nutrition in- 

 volved in the matter at all. The seeds are 

 all ready to produce the new plants, and lie 

 concealed within the apple, and cherry or 

 plum stone, waiting their season and oppor- 

 tunity. Why, then, all this big growth of 

 eatable material ? The answer is, " For the 

 birds and insects, and for any other animal 

 agencies which will help the plant on its 

 way of life." The blackbirds that peck at 

 the peaches and apples are Nature's servi- 

 tors. They come for their food to the garden- 

 er's preserves, and as they split up'the dainty 

 succulent fruit, they liberate [and scatter] 

 the seeds, and thus secure the prospect of 



