358 



Prof. J. J. Thomson on the Passage 



method being the determination of the loss of weight when 

 immersed in water. Very careful precautions were taken to 

 eliminate all trace of air from the wire and from the water by 

 placing the vessel in the receiver of an air-pump and working 

 the pump continuously for an hour or more. Care was also 

 taken to minimize the effect of capillarity, and to correct for 

 temperature in the measurements. Boiling the water by 

 passing a stream of steam through it, causing a current to 

 play on the wire, was also tried, with the result that the iron 

 and steel wires tarnished too much to render the results of 

 any great value. The effect of stretching was slightly dimi- 

 nished, a result which might possibly be due to annealing. 



Kind of Metal. 



, Percentage 

 permanent 

 elongation. 



Areas of section 

 before stretching, 

 in square centim. 



Areas of section 

 after stretching, 

 in square centim. 



Brass ■ 



German-silver ... • 



o-io 



0-20 

 012 

 0-20 



001262 

 0-01261 

 0-008255 

 0-00827 



0-01268 

 0-01269 

 0-008300 

 0-00834 



XXXVII. On the Passage of Electricity through Hot Gases. 

 By J, J. Thomson, M.A., F.R.S., Cavendish Professor of 

 Experimental Physics, Cambridge* . 



G^ASES exhibit the most remarkable differences of be- 

 haviour with respect to the passage of electricity through 

 them : the same gas under different circumstances may be 

 either an insulator and require the electromotive intensity to 

 exceed a certain value before any electricity at all can pass 

 through it, or it may be a conductor and unable to insulate even 

 a difference of potential as small as x qVo °f a Y0 ^ (Blondlot, 

 C. R. civ. p. 283). The study of the changes in the condition 

 of the gas which accompany these remarkable changes in its 

 electrical properties can hardly fail to afford most interesting 

 information as to the method by which electricity passes 

 through gases, and possibly through solids and liquids as 

 well. As one of the simplest changes which can take place in 

 the condition of a gas is that occasioned by a rise in tempe- 



* Communicated by the Author. 



