190 SELECTED NOTES FROM 



ris veskaform, whose colours I refer to diffraction, slight "thin 

 plate action," and the pressure of leaf-green or chlorophyll. The 

 elytron of Corypheria Africana, a beautiful beetle from Old 

 Calabar, which appears red in one light and blue in another, 

 cannot fully be investigated in its mounted condition ; but I 

 suspect a large part of its colour is due to a green resinoid sub- 

 stance, which could probably either be dissolved out by Ether, 

 Chloroform, or CS 2. The iridescence is due to interference by 

 diffraction. For this see "Brewster's Optics," "Ganot's Physics," or 

 " Deschanel's Natural Philosophy." 



H. POCKLINGTON. 



P.S. Nov., 1882. — The Editor has been good enough to 

 allow me to supplement the above very brief note by an abstract 

 of an article contributed to the " Pharmaceutical Journal," March 

 I St, 1873, on the "Colour of the Wing-Cases of Cantharides." 

 Cantharis vesicatoria is furnished " with two wing-covers of a 

 shining metallic green colour " (such is the B.P. description of 

 them), but when examined by lamp-light, the colour of the case 

 varies very sensibly, as the positions of the lamp and wing-case are 

 changed, and these variations are intensified if the wing-case be 

 immersed in alcohol or carbon-bisulphide (CS.^). If the test-tube 



containing the insect be held so that the lamp is between, and 

 nearly in a line with it and the eye, the colour appears no longer 

 green, but rich golden copper ; changing the position of the tube, 

 the colour passes into yellow, and quickly to green ; changing the 

 position further, the colour becomes a beautiful blue and then 

 purple. Examining the wing-case by polarised (incident) light, it 

 is found that the colour is nearly quenched in two positions of the 

 polarising prism, as it is rotated on its axis. Examining the blue 

 light with the Nicol prism, we find that in two positions of the 

 prism the colour is again nearly quenched, and that these positions 

 are complementary to those the prism occupied in the former 

 experiment. The blue colour is more intense by daylight than by 

 lamp-light, and much more intense than either by magnesium light. 

 The blue is not a pure blue, but contains a little green. This 

 blue colour is probably due to fluorescence and diffraction. The 

 small balance of light not wholly quenched by the prism was 

 examined, as it appeared to exhibit traces of a definite colouring 

 matter, to which its evident green colour was due. Specimens 

 were placed in ether, alcohol, chloroform, and carbon-bisulphide, 

 and the fluids examined spectroscopically. A sharply-defined band 

 was seen in the red, a shaded band in the green, with partial 

 passing into general absorption of the blue and violet. This 



