236 Scientific Notices — Miscellaneous. [Sept. 



low, as, for example, in those filled with water, alcohol, or oil of 

 turpentine. In others, as in those filled with a transparent solu- 

 tion of sal ammoniac and corrosive sublimate, it attains a maxi- 

 mum in the orange. Prisms of crown glass and of common 

 white glass have the maximum of temperature in the centre of 

 the red ; others, which appeared to contain lead, have the maxi- 

 mum in the limit of the red. Prisms of flint glass have the 

 maximum beyond the red. In all prisms, without exception, the 

 temperature regularly diminishes from beyond the red ; but it 

 still continues perceptible at a distance of several inches from 

 the extremest limit of that side of the visible spectrum. 

 (Schweigger's Nenes Journal, vol. x. p. 129.) 



9. Distinction of Positive and Negative Electricity. 



Positive and negative electricity may be readily distinguished 

 by the taste, on making the electric current pass by means of a 

 point on to the tongue. The taste of the positive electricity is 

 acid; that of the negative electricity is more caustic, and, as it 

 were, alkaline. Berzelius. — (Journal of Science.) 



10. Description of two Surfaces composed of Siliceous Filaments 

 incapable of reflecting Light, Sfc. 



The surface was produced by the fracture of a large quartz 

 crystal, two inches and a quarter in diameter, of a light smoky 

 colour, but impervious to the light, except in small pieces. 

 The surface of the fracture is absolutely black, and was at first 

 supposed to have been occasioned by the interposition of a thin 

 film of opaque and minutely divided matter that had insinuated 

 itself into a fissure of the crystal ; but this opinion was over- 

 turned when Dr. Brewster observed that both surfaces were 

 equally and uniformly black. He therefore suspected the phe- 

 nomenon to be occasioned by the surfaces being composed of 

 short and slender filaments of quartz, of such exceedingly mi- 

 nute diameter, as to be incapable of reflecting a single ray of the 

 strongest light; and he verified his conjecture by plunging the 

 fragment in oil of anniseeds, which approaches to quartz in its 

 refractive powers, and examining the light reflected at the sepa- 

 rating surfaces of the oil and the quartz. The blackness dis- 

 appeared ; and the fragment, whether seen by reflected or trans- 

 mitted light, comported itself like any other piece of quartz of 

 the same translucency. On removing the oil from the surface 

 it assumed its original blackness. 



Dr. Brewster calculates the diameter of the fibres to be about 

 «.__! -s-jr-n-th of an inch, or one-fourth of the thicknecs of the 

 aqueous film of a soap bubble previous to its bursting. — (Edin 

 Jour, of Science.) 







