Chemistry and Physics. 467 



4. On the Wave-length of the Double red line in the spectrum 

 of Potassium. — By means of a Rutherfurd grating ruled on glass, 

 and the electric arc, Deslandres has succeeded in measuring 

 the wave-length of the two components of the double potassium 

 line in the red, known as Ka. He finds for the stronger of the 

 two lines the value 7663-0 ten-millionths of a millimeter, and for 

 the weaker line the value 7696*3 ten-millionths; the value for D 

 being taken at 5888*9. This agrees with the value 7680*0 found 

 by Mascart for the group, that of D being 5888*0. — C. P., cvi, 

 739; J. Chem. Soc, liv, 637, July, 1888. G. f. b. 



5. Electrical discharges in gases and flames. — The observation 

 of Hertz upon the effect of the ultra violet rays upon electrical 

 discharges has awakened wide spread interest in Germany. 

 Among other workers, E. Wiedemann and H. Ebert have re- 

 peated and confirmed Hertz's results. They have also investi- 

 gated the effect of ultra violet rays upon electrical discharges 

 which are taken in various media. The source of light was a 

 Schuckert's electric arc light. It was found that the effect of the 

 ultra violet rays was greatest when the electrodes between which 

 the electrical discharge passed were of platinum. A telephone 

 was intercalated in the circuit and the character of the discharge 

 when the electrodes were in the violet rays and when they were 

 not could be readily distinguished. A glass plate which allowed 

 the violet rays to pass, but absorbed the ultra violet, immediately 

 caused the phenomenon to disappear; thus it was shown that the 

 ultra violet rays alone were effective. The effect varied with 

 the character of the electrodes, being greatest with platinum. 

 And then in the following order : zinc, copper, iron, aluminum, 

 palladium, silver. When the discharge was taken from the sur- 

 face of a liquid, the greatest effect was always obtained when 

 the liquid was capable of absorbing the ultra violet rays; The 

 authors believe that the phenomena can be attributed to the 

 selective absorption for ultra violet rays of the surfaces between 

 which the electrical discharges pass. The short wave-lengths set 

 the molecules on these surfaces into vibration and thus aid the 

 disruptive effect which is seen in the discharge. The phenomenon 

 was also investigated in G-eissler tubes and with low pressures. 

 When the electrical discharge grew rich in ultra violet rays, the 

 effects of similiar rays from the arc lamp were less noticeable. 

 The discharge was also taken between points placed in flames 

 which were colored by various salts. These salts changed the 

 character of the discharge greatly, as was evidenced by the noise 

 in a telephone connected with one of the electrodes. The greatest 

 effect was obtained from potash and from the magnesium salts, 

 thus affording another instance of the effect of ultra violet rays 

 affecting the electrodes by selective absorption. — Ann. der Physik 

 urtd Chemie, No. 10, 1888, pp. 209-264. j. t. 



6. Electro dynamic effect produced by the movement of a dielec- 

 tric in an electrical field.— W '. C. Rontgen revolved a glass or 

 vulcanite disc between two horizontal plates of a condenser, one 



