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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



stances known as pigments, and capable, when 

 present in sufficient quantity, of being extracted 

 by solvents, and used to dye or stain other bodies. 

 Such colors have not the permanence of the first- 

 mentioned class. Every entomologist knows that 

 if a case of butterflies be kept constantly exposed 

 to the sun, or even to diffused daylight, then — no 

 matter how completely air, damp, and mites, may 

 be excluded — the specimens fade, even though 

 the minute scales which clothe the wings may 

 still be found in their places. Yet the golden 

 spots on the wings of the Plusice and the pearl- 

 mother markings of the " fritillaries " remain un- 

 changed. The colors of most other insects be- 

 have in a very similar manner. Beetles are gen- 

 erally supposed to wear a more permanent livery ; 

 but every coleopterist must have observed how 

 the reds of lady-birds, of Aphodius fimetarius, of 

 Elater sanguineus, etc., lose their purity and 

 brightness on exposure, and to some extent even 

 on preservation in darkness. Even darker and 

 more intense colors are gradually affected. Thus 

 in the collection of native beetles in the British 

 Museum, which have doubtless been exposed to 

 the light for some years, the jet-black Typhosus 

 vulgaris — absurdly known as the " bull-comber " 

 — has taken a decided chestnut-brown, while a 

 similar change has come over the blue -black 

 elytra of the common dung-beetle. 



To test the speed of the bleaching power of 

 light upon deep-colored Coleoptera we placed in 

 a glass case, outside a southwestern window, spec- 

 imens of the following species : Cetonia aurata, 

 Euposcilia Australasixe, Typhosus vulgaris, Geo- 

 trupes stercorarius, Abax striola, and Sternoccra 

 orientalis ; and exposed them to the sun during 

 the months of June, July, and August, 1876. 

 The Cetonia and the Sternocera, whose colors are 

 of the interference class, were unaffected; but 

 the black of the Typhosus, the Geolrupes, and 

 the Abax, was changed to a brown, and the brown 

 of the Eupcecilia to a very dirty yellow. Thus 

 we see that even the darkest and most intense 

 pigment or absorption colors are affected by 

 light ; and this fact accounts for one class of the 

 variations which are met with in different speci- 

 mens of one and the same species. An insect 

 that has lived long, and has been much exposed to 

 the sun, may have more degraded colors than 

 such as are captured soon after reaching full per- 

 fection. 



If we examine the nature of the changes 

 produced by the action of light, we shall notice 

 the following facts : Pigment greens, blues, lilacs, 

 pinks, and roses — shades not very abundant in the 



animal kingdom — are the first to fade. Full reds, 

 purples, and blacks, resist longer. Oranges, yel- 

 lows, fawns, drabs, browns, and olives, have still 

 greater permanence, merely taking a duller or 

 dirtier tone. The changes ensue in a definite di- 

 rection. Blues and pale greens turn to a gray or 

 a yellowish drab ; darker greens to an olive ; 

 lilacs, pinks, and roses, to various shades of gray; 

 reds become a reddish or yellowish brown; pur- 

 ples a very dirty brown ; yellows and oranges 

 verge more to a pale brown, and may rank as 

 buffs or fawns. The alteration is, therefore, from 

 the primary or secondary toward the tertiary 

 colors, accompanied with a decrease in depth. 

 But we have never seen a primary color, when 

 fading under the influence of light, pass into an- 

 other primary color ; nor does any secondary or 

 tertiary color ever pass into a primary. The 

 change which blacks undergo will not seem sur- 

 prising if we reflect that in Nature, as well as in 

 art, they generally consist of an intense olive or 

 brown to which a deep blue or purple is super- 

 added. The latter hues, being the more fugitive, 

 fade first on exposure to light, and thus a dirty 

 olive or a rusty brown must remain. 



These changes are in partial harmony with 

 what we observe in the vegetable kingdom. A 

 dull, dirty brown is the ultimate goal toward 

 which leaves, flowers, and fruits, as well as in- 

 sects, tend while fading; but those splendid in- 

 termediate changes which we find in autumnal 

 foliage have nothing analogous in the decaying 

 colors of insects. 



It is curious that in the manufacture of those 

 artificial colors which now play so important a 

 part in tinctorial operations a corresponding rule 

 holds good. If these dyes, during their elabora- 

 tion, are submitted to a heat too high or too pro- 

 longed, the product becomes dusky, and a dirty 

 brownish gray is the final result. 



We must further note how, in the animal and 

 vegetable kingdoms, pure and bright colors an/ 

 connected with the highest vitality only. We 

 plant the dusky seed in the earth amid the dark 

 remains of decomposing organic matter, and as 

 it grows up we see it put on higher and higher 

 colors, till, in the culminating moment of its life, 

 in the act of inflorescence, prismatic hues are all 

 but universal. Then begins the process of de- 

 cay, attended by a degradation of color. Similar 

 changes may be traced in animals. Externally 

 we need merely compare the dull-colored larva 

 with the brilliant imago, or the sombre-coated 

 nestling with the brighter plumage of the mature 

 bird. Internally we may contrast the intensely- 



