384 Intelligence and Miscellaneous Articles. 



according to its position. It will thus be seen that the calibration 

 of instruments of this kind must not be forgotten when they are 

 moved from one place to another. — Journal de Physique, Jan. 1887. 



ON METALLIC LAYERS WHICH RESULT FROM THE VOLATILIZA- 

 TION OF A KATHODE. BY BERNHARD DESSAU. 



The results of the present investigation may be summed up as 

 follows : — 



By appropriate electrical discharge in highly rarefied spaces, the 

 metal which acts as kathode is volatilized and settles on a glass plate 

 as a reflecting layer or mirror. If the oxygen has not been most 

 carefully removed, all metals seem to undergo oxidation under these 

 circumstances. There is perhaps in all cases a combination with 

 the traces of residual gas (hydrogen or nitrogen), yet the mirrors 

 obtained in hydrogen are not materially different from those of pure 

 metals. With suitable arrangement of the electrodes the layer of 

 metal is obtained as a flat cone ; and when viewed in reflected light, 

 under as acute an angle as possible, coloured interference-rings are 

 obtained, which prove the presence of a dispersion in the metals. It 

 may be concluded with some certainty that this dispersion is normal 

 in platinum, iron, nickel, and silver, and abnormal with gold and 

 copper. The layer directly produced by the discharge, whether it 

 be metal or oxide, is always double refracting, probably in conse- 

 quence of an electrical repulsion between the particles expelled, and 

 the regular stratification thereby produced ; in the metals the ray 

 which vibrates tangentially is accelerated in respect of the others. 

 In the metals the cross of double refraction was also observed in 

 reflected light, and in reflection from the metal side the action 

 was the reverse, and from the glass side the same as in transmitted 

 light. Double refraction disappears on oxidation of the double- 

 refracting metals, as well as by reduction of the layers of oxide, 

 while heating without any chemical change has no effect. — Wiede- 

 mann's Annalen, No. 11, 1886. 



ON THE PASSAGE OF THE ELECTRIC CURRENT THROUGH AIR 

 UNDER ORDINARY CIRCUMSTANCES. BY J. BORGMANN. 



One end of the coil of a Wiedemann's galvanometer is connected 

 with the earth, and the other with a platinum wire, which is placed 

 in the flame of an insulated spirit-lamp. At a distance of 1^ metre 

 from this lamp is an ordinary Bunsen burner, which is connected 

 with a conductor of the Holtz machine ; the other conductor is put 

 to earth. 



When the lamp is lighted the galvanometer indicates no current ; 

 but when the disk is rotated a distinct current at once appears in 

 the galvanometer, and the deflection of the needle does not alter so 

 long as the machine works at a uniform rate. If the Bunsen 

 burner is connected with the other conductor of the machine, a 

 current in the opposite direction is at once set up. — Beiblatter cler 

 PhysiJc, January 1887. 



