PDF - Wallace Online
PDF - Wallace Online PDF - Wallace Online
354 TROPICAL NATUREMr. Darwin's Descent of Man, chapters x. to xviii., and tochapters iii. iv. and vii. of the first portion of the presentvolume.Normal ColoursThe fourth group of normally coloured animals includesall species which are brilliantly or conspicuously coloured inboth sexes, and for whose particular colours we can assign nofunction or use. 1 It comprises an immense number of showybirds, such as kingfishers, barbets, toucans, lories, tits, andstarlings ; among insects most of the largest and handsomestbutterflies, innumerable bright-coloured beetles, locusts, dragonflies,and hymenoptera ;a few mammalia, as the zebras ;agreat number of marine fishes ;thousands of striped andspotted caterpillars ;and abundance of mollusca, star-fish, andother marine animals. Among these we have included somewhich, like the gaudy caterpillars, have warning colours but;as that theory does not explain the particular colours or thevaried patterns with which they are adorned, it is best toinclude them also in this class. It is a suggestive fact thatall the brightly-coloured birds mentioned above build in holesor form covered nests, so that the females do not need thatprotection during the breeding season which I believe to beone of the chief causes of the dull colour of female birds whentheir partners are gaily coloured. This subject is fully arguedin chapter vi. of the present volume.Leaving the colours of flowers to be discussed in anotherchapter, we will now consider how the general facts of colourhere sketched out can be explained. We have first to inquirewhat is colour, and how it isproduced j secondly, what isknown of the causes of change of colour ; and, lastly,whattheory best accords with the whole assemblage of facts.The Nature of ColourThe sensation of colour is caused by vibrations or undulationsof the ethereal medium of different lengths and velocities.The whole body of vibrations caused by the sun is termed* Distinctness of marking for purposes of recognition is probably the usein all cases. See p. 367, and Darwinism, p. 217.
v COLOURS OF ANIMALS 355radiation, or, more commonly, rays ;and consists of sets ofwaves which vary considerably in their dimensions and rateof recurrence, but of which the middle portion only is capableof exciting in us sensations of light and colour. Beginningwith the largest waves, which recur at the longest intervals,we have first those which produce heat-sensations only ;asthey get smaller and recur quicker, we perceive a dull redcolour ;and as the waves increase in rapidity and diminish insize, we get successively sensations of orange, yellow, green,blue, indigo, and violet, all fading imperceptibly into eachother. Then come more invisible rays, of shorter wavelengthand quicker recurrence, which produce, solely orchiefly, chemical effects. The red rays, which first becomevisible, have been ascertained to recur at the rate of 458millions of millions times in a second, the length of each wave-being ?6 ^ 60 of an inch ;while the violet rays, which lastremain visible, recur 727 millions of millions times per second,and have a wave-length of a ^ lfl of an inch. Although thewaves recur at different rates, they are all propagated throughthe ether with the same velocity (192,000 miles per second) ;just as different musical sounds, which are produced bywaves of air of different lengths and rates of recurrence, travelat the same speed, so that a tune played several hundredyards off reaches the ear in correct time. There are, therefore,an almost infinite number of different colour-producingundulations, and these may be combined in an almost infinitevariety of ways, so as to excite in us the sensation of all thevaried colours and tints we are capable of perceiving. Whenall the different kinds of rays reach us in the proportion inwhich they exist in the light of the sun, they produce thesensation of white.If the rays which excite the sensation ofany one colour are prevented from reaching us, the remainingrays in combination produce a sensation of colour often veryfar removed from white. Thus green rays being abstractedleave purple light; blue, orange-red light; violet, yellowishgreenlight, and so on. These pairs are termed complementarycolours. And if portions of differently colouredlights are abstracted in various degrees, we have produced allthose infinite gradations of colours, and all those varied tintsand hues which are of such use to us in distinguishing
- Page 320 and 321: 304 TROPICAL NATUREshine they more
- Page 322 and 323: TROPICAL NATUREMAMMALIAMonkeysThe h
- Page 324 and 325: TROPICAL NATUREacross the expanded
- Page 326 and 327: 310 TROPICAL NATURErather in the un
- Page 328 and 329: IVHUMMING-BIRDSAS ILLUSTEATING THE
- Page 330 and 331: 314 TROPICAL NATUREover the lower a
- Page 332 and 333: 316 TROPICAL NATUREhumming-birds ma
- Page 334 and 335: 318 TROPICAL NATUREsweets, in all t
- Page 336 and 337: TROPICAL NATUREDisplay of Ornaments
- Page 338 and 339: 322 TROPICAL NATUREtamed a number o
- Page 340 and 341: TROPICAL NATUREallied species on Ch
- Page 342 and 343: TROPICAL NATUREvariation, and with
- Page 344 and 345: TROPICAL NATUREhalf completed.In th
- Page 346 and 347: TROPICAL NATUREdevelopment; the for
- Page 348 and 349: TROPICAL NATUREsoft, while the tong
- Page 350 and 351: 334 TROPICAL NATUREtubular tongue o
- Page 352 and 353: TROPICAL NATURElittle white-eyes (Z
- Page 354 and 355: THE COLOURS OF ANIMALS AND SEXUAL S
- Page 356 and 357: 340 TROPICAL NATUREand emotions may
- Page 358 and 359: 342 TROPICAL NATUREIt is true that
- Page 360 and 361: 344 TROPICAL NATUREprotecting them
- Page 362 and 363: 346 TROPICAL NATUREThis caterpillar
- Page 364 and 365: 348 TROPICAL NATUREweed of these tw
- Page 366 and 367: 350 TROPICAL NATUREflies, so that i
- Page 368 and 369: 352 TROPICAL NATUREThe universal av
- Page 372 and 373: 356 TROPICAL NATUREexternal objects
- Page 374 and 375: 358 TROPICAL NATUREand Mr. Sorby ha
- Page 376 and 377: TROPICAL NATUREment are much more n
- Page 378 and 379: 362 TROPICAL NATUREprotective, serv
- Page 380 and 381: TROPICAL NATUEEincreasing complexit
- Page 382 and 383: 366 TROPICAL NATUREmale to special
- Page 384 and 385: TROPICAL NATURErunning to its burro
- Page 386 and 387: 370 TROPICAL NATUREturkey, and the
- Page 388 and 389: 372 TROPICAL NATUREghost-moth may r
- Page 390 and 391: 374 TROPICAL NATUREwhite companions
- Page 392 and 393: 376 TROPICAL NATUREtion, and what m
- Page 394 and 395: 378 TROPICAL NATURENatural Selectio
- Page 396 and 397: TROPICAL NATUREaway with the rapidi
- Page 398 and 399: 382 TROPICAL NATUREhere, not only i
- Page 400 and 401: 384 TROPICAL NATUREyet, as none of
- Page 402 and 403: 386 TROPICAL NATURE vmetallic colou
- Page 404 and 405: 388 TROPICAL NATUREThe Andaman isla
- Page 406 and 407: 390 TROPICAL NATUREpum, while black
- Page 408 and 409: TROPICAL NATUREthe large brilliantl
- Page 410 and 411: 394 TROPICAL NATUREzones ;while, es
- Page 412 and 413: 396 TROPICAL NATUREthese differ gre
- Page 414 and 415: 398 TROPICAL NATUREvery minute and
- Page 416 and 417: 400 TROPICAL NATUREsmall brown seed
- Page 418 and 419: TROPICAL NATUREdetails of these ada
354 TROPICAL NATUREMr. Darwin's Descent of Man, chapters x. to xviii., and tochapters iii. iv. and vii. of the first portion of the presentvolume.Normal ColoursThe fourth group of normally coloured animals includesall species which are brilliantly or conspicuously coloured inboth sexes, and for whose particular colours we can assign nofunction or use. 1 It comprises an immense number of showybirds, such as kingfishers, barbets, toucans, lories, tits, andstarlings ; among insects most of the largest and handsomestbutterflies, innumerable bright-coloured beetles, locusts, dragonflies,and hymenoptera ;a few mammalia, as the zebras ;agreat number of marine fishes ;thousands of striped andspotted caterpillars ;and abundance of mollusca, star-fish, andother marine animals. Among these we have included somewhich, like the gaudy caterpillars, have warning colours but;as that theory does not explain the particular colours or thevaried patterns with which they are adorned, it is best toinclude them also in this class. It is a suggestive fact thatall the brightly-coloured birds mentioned above build in holesor form covered nests, so that the females do not need thatprotection during the breeding season which I believe to beone of the chief causes of the dull colour of female birds whentheir partners are gaily coloured. This subject is fully arguedin chapter vi. of the present volume.Leaving the colours of flowers to be discussed in anotherchapter, we will now consider how the general facts of colourhere sketched out can be explained. We have first to inquirewhat is colour, and how it isproduced j secondly, what isknown of the causes of change of colour ; and, lastly,whattheory best accords with the whole assemblage of facts.The Nature of ColourThe sensation of colour is caused by vibrations or undulationsof the ethereal medium of different lengths and velocities.The whole body of vibrations caused by the sun is termed* Distinctness of marking for purposes of recognition is probably the usein all cases. See p. 367, and Darwinism, p. 217.
Change language