On the Electrical Resistance of Gases. 201 



versely proportional to the section of the conductor. G. Wiede- 

 mann has proved, by experiments *, that the tension which is 

 necessary upon the electrodes in order to force the electricity 

 of a Holtz machine to traverse a cylindrical tube filled with 

 rarefied gas is independent of the radius of the tube- — which 

 means, in other terms, that the electrical resistance of the gas 

 is independent of the section of the tube. In two experi- 

 ments, one with a tube 16 millim. and the other with a tube 

 05 millim. in diameter, Schulzf found only an insignificant 

 difference in the electrical tension requisite to compel the elec- 

 tricity of a Holtz machine to pass through the tube. 



5thly. With solid and liquid conductors, the difference 

 between the electroscopic tensions on two points situated at a 

 certain distance the one from the other is proportional to the 

 product of the resistance between those points multiplied by 

 the intensity of the current. Warren De la Rue and Hugo 

 Mullerl, have, on the contrary, proved experimentally that 

 the difference between the electroscopic tensions at two points 

 situated at a distance from one another in a column of gas is 

 totally independent of the intensity of the current. These 

 physicists caused the current of a battery composed of a great 

 number of elements to vary between very wide limits ; and 

 yet it was impossible to perceive any variation in the above- 

 mentioned difference. With the aid of a galvanic battery of 

 great electromotive force, Hittorf has also proved, although 

 in another way, that the difference between the electric ten- 

 sions of the electrodes conducting to the column of gas is inde- 

 pendent of the intensity of the current §. When for the 

 column of gas between the electrodes a liquid conductor was 

 substituted, the difference became, as might have been ex- 

 pected, proportional to the intensity of the current. From 

 this Hittorf draws the conclusion, somewhat prematurely, that 

 the resistance of the column of gas must be in the inverse pro- 

 portion of the intensity of the current, to which circumstance 

 he attributes a fundamental importance for the conductivity 

 of gases. 



6thly. Several years since, Edm. Becquerel proved ||, by 

 experiments, that gases begin to be conductors when heated 

 to the temperature of redness, after which their conductivity 

 increases in proportion as the temperature rises above that 

 point. If the temperature is sufficiently elevated, they even 

 let the feeble current of a single element pass. The conducti- 



* Pogg. Ann. clviii. p. 53 (1876). f Ibid, cxxxv. p. 254 (1868). 



% Comptes Rendus, lxxxvi. p. 1072 (1878). 



§ Wied. Ann. vii. p. 573 (1879). 



|| Ann. de Ch. et dc Ph. [3] xxxix. p. 377 (1853). 



Phil. Mag. 8. 5. Yol. 13. No. 80. March 1882. R 



