84 



COLOUR. 



direction, on reaching a solid body, part of the undula- 

 tions must proceed forward into the interstices of the 

 body, and part, as from a new centre of motion, are 

 transmitted back into the air; in the former case they 

 are refracted, and the amount of refraction depends 

 entirely on the diminished velocity of the propagation 

 of the undulations within the refracting medium ; in 

 the latter they are reflected ; furthermore, when light 

 is absorbed, the ethereal waves are presumed to be 

 broken and scattered in dispersed undulations through 

 the interior of the body (Herschel) ; hence the ordi- 

 nary properties of light may by either theory be 

 explained ; there are, however, certain phenomena, 

 or appearances which light may be brought to exhibit, 

 which are explicable only upon the undulatory theory, 

 one in particular already adverted to is what is termed 

 the interference of light, 



It was shown by Arago and Fresnel, that when two 

 diverging beams are made to cross at a very small 

 angle, instead of giving rise to a double illumination 

 at the point where they mix, they exhibit a space 

 striped with alternate black and bright bands. Here, 

 therefore, we have the paradoxical result of two con- 

 spiring rays of light, producing absolute darkness, 

 which is inexplicable by the molecular or Newtonian 

 theory ; but which is a direct consequence of the 

 theory of undulations, according to which it is obvious 

 that when two waves, propagated from different origins, 

 meet in such a manner that the hollow of the one 

 coincides with the elevation of the other, and the 

 elevation of the one with the hollow of the other, 

 the two waves must obliterate or destroy one another. 

 Accordingly, the point remaining at rest, where the 

 antagonism occurs must appear dark, the agitation of 

 the ethereal medium being necessary to affect our visual 

 organs with the sense of light and colour. Upon this 

 interference of light the beautiful phenomena of pe- 

 riodical colours, or those exhibited by thin plates, 

 appear also to be dependent. In this case a new 

 divergence is given to some of the waves, while others 

 pass on unaltered. 



According, therefore, to the undulatory theory, 

 colour is an effect produced by the vibrations of the 

 ethereal medium, which affects us when in undulation 

 with the sense of light, and the difference of the 

 colours so produced depends on the greater or lesser 

 frequency of the vibrations, the whole scale of colours 

 from violet to crimson lying between vibrations which 

 are four hundred and fifty-eight million millions, and 

 seven hundred and twenty-seven million millions in a 

 second ; a proportion it may be observed smaller than 

 the ratio of undulations which takes place in the 

 production of perceptible sounds. As in sound the 

 pitch or note is determined by the frequency of the 

 aerial pulses, so according to the undulatory theory 

 the colour is determined by the frequency of the 

 ethereal pulses. 



1. WHIT*. 



1. Snww white is the characteristic colour of the whites, 

 being free of all intermixture it resembles new fallen snow. 

 Animal, breast of black-headed gull ; vegetable, the snow- 

 drop ; mineral, Carrara marble. 



2. Reddish white (snow white, with a minute portion of 

 crimson red and ash erey). Animal, egg of grey linnet; vege- 

 table, back of the Christmas rose ; mineral, porcelain earth. 



3. Purplish white (snow white, with the slightest tinge of 

 crimson red and Berlin blue, and a very minute portion 



Whichever of these theories be adopted, the natu- 

 ralist should acquire the power of discriminating with 

 accuracy the distinction between every variety of 

 colour, however blended, otherwise his descriptions, 

 whether of animals, vegetables, or minerals, will be 

 imperfect. It is true, that the majority of mankind 

 readily distinguish the more obvious colours, red, 

 yellow, blue ; but the combinations these may assume 

 are so numerous, and the tints so delicate, that they 

 cannot be adequately appreciated excepting by a 

 practised eye. Hence an artist will perceive beauties 

 in a landscape which escape the notice of an ordinary 

 observer. It is desirable therefore that the naturalist 

 should commence his studies by learning to distin- 

 guish accurately the different colours of natural bodies ; 

 he should apply to each of these a definite and correct 

 term, expressing even the very shade it may present ; 

 and he should know how the simple and elementary 

 colours may be so combined as to produce the suc- 

 cession of tints observable in shells and minerals, in 

 the plumage of birds, the petals of flowers, and which 

 bathe with beauty at sunrise or sunset the earth, the 

 ocean, and the heavens. He will find that the colours 

 which adorn the face of nature pass in suites into one 

 another ; nor can any thing be more exquisite than 

 the effect produced by their blending together in 

 mutual harmony. The eminent Werner directed his 

 attention to forming a nomenclature of colour, which 

 has been adopted by Professor Jamieson, and adapted 

 to the study of botany, zoology, and meteorology, bv 

 Mr. Syme. The original suite of colours was by- 

 Werner fixed at seventy-nine ; but finding the num- 

 ber defective when applied in the study of zoology and 

 botany, it was extended by Mr. Syme to a hundred and 

 ten. " The method of classification adopted by Werner 

 was," says Professor Jamieson, " simple and elegant. 

 He placed together all those varieties which contained 

 the same principal colours in a preponderating quan- 

 tity, and he then arranged them in such a manner 

 that the transition of the one variety into the other, 

 and of the principal into the neighbouring colours 

 was preserved, so that by mere ocular inspection any 

 person, accustomed to discriminate colours correctly, 

 can analyse the different varieties of colour which 

 occur in the mineral kingdom." In this system as 

 improved by Syme, there are ten principal colours, 

 each of which contains one that is called the charac- 

 teristic colour ; thus snow is the characteristic colour 

 of white, velvet-black of black, Berlin-blue of blue, 

 emerald-green of green, &c., and this characteristic 

 colour is so placed in the scale that, ascending or 

 descending from it, we may trace the colours which 

 are connected by transition. The following is the 

 mproved nomenclature of the Wernerian system by 

 Syme ; it explains how the gradations of colour are 

 produced, and illustrates them individually by refer- 

 snce to some animal, vegetable, or mineral *. 



of ash grey). Animal, junction of the neck and back of the 

 kittiwake gull ; vegetable, white geranium ; mineral, arragonite. 



4. Yellowish white ( snow white, with a very little lemon 

 yellow and ash grey). Vegetable, hawthorn blossom ; mineral, 

 chalk and Tripoli. 



5. Orange coloured white (snow white, with a very small 

 portion of tile red and king's yellow, and a minute portion 

 of ash grey). Animal, breast of white owl, or screech owl ; ve- 

 getable, large wild convolvulus ; mineral, French porcelain clay. 



6. Greenish white (snow white, mixed with a very little 



Syme on Werner's Nomenclature of Colours. 



