Intelligence and Miscellaneous Articles. 219 



was further found that platinum electrodes of 10 to 20 square 

 eentim. surface, which Kohlrauseh found quite sufficient for mea- 

 suring the resistance of liquids, are by no means adequate with 

 the human body to produce a cessation of the tone in the telephone 

 in any position Avhatever. It was only when the surface of con- 

 tact between the metal and the moist hand was increased to several 

 hundred square centimetres that the tone ceased, or at any rate 

 there was a very pronounced meniscus. The surface necessary 

 varies with the region of the body. In order uniformly to moisten 

 large surfaces of the body, they were immersed in troughs through 

 which the current was passed by cleanly polished zinc plates. In 

 such conditions the resistance of the body was found to be very 

 small (from hand to hand 3-400 ohms), and, as was to be expected, 

 independent of the induction-currents. 



In order to utilize the method for electrodiagnostics, in which a 

 very small electrode is always used, the author replaces the metal 

 rheostat by a liquid one (platinum in dilute sulphuric acid), the 

 immersed metal surface being very small. There must be a definite 

 ratio between this surface and the surface of the skin touched by 

 the electrode, to produce a cessation of the tone — that is, when the 

 displacement of phase of the electrical vibrations is to be equalized. 

 The graduation of the rheostat is a difficult matter, and it of 

 course is only available for certain strengths of current. From 

 observations of the author, it appears probable that the seat of 

 polarization is mainly, if not exclusively, in the uppermost layers 

 of the skin. — Beiblalter der Physik, No. 4, 1892 ; from Verhandl. 

 des X. Congr.fur inner e Medizin Wiesbaden, 1891. 



ELECTRIFICATION OF A GAS IN THE GLOW-DISCHARGE. BY 



L. WARBURG. 



The results of this investigation may be summed up as follows : — 



1 . The electrostatic attraction w'hich a plane kathode experiences 

 during the glow-discharge may be measured by the balance, and 

 from this the electrical force and the surface-density at the cathode 

 surface may be calculated. That attraction is found to be propor- 

 tional to the surface-density, and amounts, in milligrammes per 

 ampere, for bright platinum and aluminium kathodes in 



Drv nitrogen from 0*5 to 2 mm. pressure, 1300 to 2400. 



Slightly moist nitrogen „ 0-5 „ 2 „ 500 „ 800. 



Hydrogen „ 1 „ 3 „ 200 „ 350. 



2. In the negative glow-light there is, as Schuster has shown*, 

 an excess of free positive electricity. The amount of this positive 

 charge is equal and opposite to the negative charge of the ka- 

 thode. Like this discharge it is proportional to the square root 

 of the current density, and has been found to be of the order 



10 -)0 '- — : — for 1 milliampere per square centimetre with 



square eentim* 

 bright platinum and aluminium kathodes in nitrogen and hydrogen. 



* Proc. Eoy. Soc. vol. xlvii. p. 541 (1890). 



