1 (> O B S E R V A T I O N S 



spines, the ventral fin (near the head) has sixteen, 

 the pectoral ten, the anal fourteen, and the tail 

 eighteen. 



o 



He sometimes grows to about three pounds in 

 weight, though one of a pound and a half is con- 

 sidered a good sized fish, and larger are not very 

 often caught with the fly, the usual weight being 

 from two ounces to a pound of those which rise 

 freely to it. The fish of the 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, except the belly, which is white or nearly 

 so, but the scales often exhibit by deflected 

 light a great variety of colours dependant upon 

 the positions chosen to view them from.* The 



* From a very curious series of experiments detailed by Sir David 

 Brewster in his Treatise on Optics, (p. 113 et seq.) " it is obvious that 

 the splendid colours of mother of pearl, &c. are produced by a parti- 

 cular 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 

 articles of female embellishment, are the result of machinery constructed 

 on this grooving principle, upon which, we believe, depends the above 

 mentioned and many similar phenomena (as in the peacock's feather, &c.) 

 In sun, gas, or candle-light some iris ornaments rival " the brilliant 

 flashes of the diamond." (A superb example of a grooved medallion 

 may be seen in the library of the Royal Institution). But in day light 

 and in ordinary circumstances the colours of the iris ornaments are not 

 easily distinguished. 



