Intelligence and Miscellaneous Articles. 297 



In exceptional cases it is possible to produce such a thin coating 

 that the extreme edge is fringed with a faint blue. 



The other case, lead, is now easily explained. This metal gives 

 a coating of which the colour is a beautiful chrome yellow : and 

 regarding this merely as a repetition of the preceding phenomenon, 

 and the yellow as compounded of rays from the whole range of the 

 spectrum but not in the proper proportion to form white, the line of 

 thought suggested evidently is that, if the layer be decreased in 

 thickness regularly from the centre to the circumference of the 

 charcoal, there ought to be, at some distance from the centre, a 

 zone within which sufficient red should be transmitted to equalize 

 the amount of blue lost by absorption, and the reflected rays should 

 form a yellowish white. Beyond this, as the thickness of layer 

 still decreased, the colour should be blue for the same reason as in 

 the case of antimony. The white zone is easily produced ; and the 

 blue border which always surrounds it polarizes the light as 

 before and transmits orange-coloured rays. 



The theory, once given, serves to explain nearly all the anoma- 

 lous colourings of the charcoal coatings, the bluish borders which 

 occasionally skirt almost any of the metallic oxides, the " peacock- 

 tails" of cadmium, etc., and thus does away with the necessity 

 of supposing the presence of impurities (though, by the way, no im- 

 purity would solve the problem in the case of the cadmium green.) 



From a physical standpoint, the experiments seem interesting as 

 an extension of our knowledge of the action of these small particles 

 upon light. Had not the subject presented itself in this way, we 

 would scarcely have guessed that such a change in reflecting-power 

 could have been produced by so small a change in size and 

 thickness. — Silliman's American Journal, September 1880. 



Baltimore, Md., July 9 ; 1880. 



ON AN AREOMETER FOR DETERMINING THE DENSITY OF SOLID 

 BODIES. BY M. BUGUET*. 

 The author makes the rod of a Nicholson's areometer thicker and 

 longer than it usually is, denotes by o and n the depth to which it 

 sinks when unloaded and when loaded with n grams, and graduates 

 the interval into parts corresponding to cubic centimetres and their 

 subdivisions. If, when the body to be investigated is on the upper 

 pan the areometer sinks to the division-mark P, and when on the 



P 



lower to P', the specific gravity is ^ — tjt. — "Wiedemann's Beiblatter, 



1880, No. 7, p. 497. r ~ r 



DETERMINATION OF THE SPECIFIC GRAVITY OF SMALL FRAG- 

 MENTS OF MINERALS. BY J. THOULETf . 

 A solid body is pressed into a small ball of wax, so that the mean 



* Journ. cle Phys. ix. pp. 93, 94 (1880). 



t Z.-S.f. Kryst. iv. p. 421 (1880) ; Bull. Soc. Min. ii. p. 189 (1879), 



Phil. Mag. S. 5. Vol. 10. No. 62. Oct. 1880. Y 



