ON THE GRAYLING. 19 



spawn of April or May (measuring 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. 1 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 

 grey 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 off 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 



1 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 ins ornaments on brass and other metal buttons, and orna- 

 ments of dress, are the result of machinery constructed on this 

 grooving principle, upon which, we believe, depend similar pheno- 

 mena in the peacock's feather, &c. In sun, gas, or candle-light 

 some iris ornaments rival " the brilliant flashes of the diamond." 



c 2 



