68 Scientific Intelligence. 



increase of sparking distance ; and that the potential difference at 

 the electrode is nearly independent of the current strength if the 

 discharge is of the nature of a brush. The G. Wiedemann-Hittorf 

 law for Geissler tube discharges therefore holds also for brush 

 discharges in free air. — Wied. Ann., No. 12, 1898, 660-675. 



The writer has substantiated the results of Toepler, as far as 

 relates to the stratification, by the employment of an apparatus 

 which can produce a difference of potential of three million volts. 

 The stratification with this high voltage occurs in the neighbor- 

 hood of the positive pole. j. t. 



8. The Spectrum of Lightning. — Photographs of the light of a 

 spark six feet in length, taken in the Jefferson Physical Labora- 

 tory, show atmospheric lines very strongly developed between E 

 and H. No more lines were produced by a voltage of three 

 million than can be brought out with a voltage of one hundred 

 thousand. With the higher voltage, however, there is a complete 

 absence of the metallic lines of the terminals. The photographs 

 taken with the high voltage therefore must closely resemble the 

 spectrum of lightning. j. t. 



9. Dispersion in the Electrical Spectrum. — Observations on di- 

 electric constants for periods between wave lengths 2 cm to 75 cra have 

 hitherto been wanting. E. Marx has endeavored to supply this 

 break in the subject and has applied to his results certain laws of 

 dispersion. He speedily ascertained that in order to obtain very 

 short electrical waves it is necessary to so interlock the primary 

 and secondary circuits, or in other words the exciting and reso- 

 nating circuits, in such a manner that only the fundamental vibra- 

 tions of the primary circuit were in evidence. He employed 

 Drude's method of measurement, which consists in nodes measure- 

 ing the displacement of the electrical waves on wires, when a 

 portion of these wires are surrounded by a dielectric. By means 

 of an exciter of small dimensions he obtained electrical waves, 

 4 cm , 36 cm , and 58 cm in length. The positions of the nodes were 

 ascertained by means of a Zehnder-Geissler tube. The index of 

 refraction of electric waves, 3*2 cm in length, for water was found 

 to be 



* n* = 85-0 (atl7°C.) 

 For wave length 36 cm 



n"= 82-50 (at 17° C.) 

 For wave length 53 cm 



n 2 =83-13 (at 17° C.) 

 The indices of refraction of ethyl-alcohol were similarly inves- 

 tigated. It was surmised that absorption bands of great extent 

 in the ultra-red modify existing dispersion formulae. A difference 

 in concentration of the ethyl-alcohol solutions of 1 per cent can 

 change the square of the electrical index of refraction 35 per cent. 

 — Wied. Ann.,^o. 11, 1898, pp. 411-434; ibid., No. 12, 1898, pp. 

 597-622. j. t. 



10. Traite J^lementaire de Mechanique Chimique fondee sur la 

 Thermodynamique par P. Duhem. Tome iii, Les Melanges 



