Intelligence and Miscellaneous Articles. 295 



sary, and that we may form quite a distinct idea of the nature 

 of thermo-electricity when viewed from a different standpoint. 



When we consider that the theory of the galvanic cell as at 

 present existing rests altogether on the assumption of voltaic 

 contact force, we may well expect the most radical changes in 

 this direction ; and, so far as I can at present see, the theory 

 of the cell may be represented in a considerably simpler 

 manner and on more natural principles than heretofore. 



The results of a more searching investigation of these 

 matters shall be reserved for future publication. 



XXXVII. Intelligence and Miscellaneous Articles. 



THE COLOUES OF THIN BLOWPIPE DEPOSITS. BY C. H. KOYL, 

 B.A., STUDENT OF PHYSICS IN JOHNS HOPKINS UNIVERSITY. 



SOME examples of the action of very fine particles of matter upon 

 light having lately come to my notice, it may be interesting to 

 make them public, as they have heretofore, I believe, been unex- 

 plained. 



Those who are familiar with the methods of blowpipe analysis 

 have observed faint borders occasionally surrounding some of the 

 coloured charcoal coatings, the colours of these borders seemingly 

 bearing no relation to the characteristic colours of the adjoining 

 oxides. For instance, the white coating of antimony is generally 

 accompanied with a blue border, the brownish oxide of cadmium 

 occasionally with a green, while the lead and bismuth yellows not 

 unfrequently have a whitish ring inclosing them. As these occur 

 only and always where the coating is very thin, they have a 

 significance different from that of the ordinary colours, and as 

 they may be produced at pleasure from the purest specimens, they 

 cannot be due to mixtures of the metals. A possible analogy with 

 the antimony blue was suggested by a consideration of the colours 

 of the sky ; and to prove the connection, it was simply necessary 

 to show the similarity of attendant phenomena. As is well known, 

 it is believed that the blue of the sky is due to the presence in 

 the atmosphere of suspended particles so fine that they are unable 

 to reflect the longer rays of the spectrum, which accordingly are 

 transmitted, and the union of the remainder gives to the sky its 

 blueness. At evening the sky is red because we get the rays of 

 the sun directly transmitted or reflected from the clouds. Thirdly, 

 the light of the sky, reflected at an angle of 90° with the sun, is 

 plane-polarized. 



"When an antimony coating had been produced which gave, 

 beyond the white oxide, a blue well defined and full, the whole 

 was illuminated in a dark room by a sodium flame ; and that the 

 blueness was no psychical or physiological effect as distinguished 

 from ordinary vision, was proved by the fact that here it almost 



