ON THE GRAYLING. 19 



spawn of April or May (raeasui'ing from the 

 nose to the fork of the tail) grows to about six 

 inches by the next April. 



A general tint, which may be called a light 

 blue silvery grey, pervades nearly the whole 

 surface of his body, excepting the belly, which 

 is white or nearly so, but the scales often exhibit 

 iridescent hues, of great beauty.^ The back and 

 head are of a much darker grey, but its com- 

 ponents cannot, perhaps, be described verbally. 

 Some lines of brown are intermixed with the 

 gre}^ of the sides, and a few black spots are seen 

 near the shoulder. The back fin has a purplish 

 tint studded with large dark spots, the other fins 

 are not so red as those of the Trout, but have 

 more yellow-brown in them shaded ofi' with 

 purple. The tail is a kind of slate colour. The 

 colours vary a little in different waters, and 

 unlike the Trout, the better the condition, the 



^ From a very curious series of experiments detailed by Sir 

 David Brewster in his excellent treatise on optics (p. 113 et 

 seqq.) "it is obvious that the splendid colours of mother-of-pearl, 

 &c., are produced by a peculiar configuration of surface ; and by 

 examining this surface with microscopes, he discovered in almost 

 every specimen a grooved structure like the delicate texture of 

 the skin at the top of an infant's finger," &c. By cutting 

 grooves upon steel at the distance of from the 2,000th to the 

 10,000th of an inch apart, Mr. Barton produced still more 

 brilliant hues, and his iris ornaments on brass and other metal 

 buttons, and ornaments of dress, are the result of machiiiery 

 constructed on this grooving principle, upon which, we believe, 

 depend similar phenomena in the peacock's feather, &c. In 

 sun, gas, or candle-light some iris ornaments rival •' the brilliant 

 flashes of the diamond." 



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