Disjunction- currents through Gases of various Densities. 23 



If, now, the conducting-power of the gas, as is probable, increases, 

 and the duration of the spark lengthens, when the gas is rarefied, 

 the result obtained (that the deflections first decrease and then 

 increase) contains nothing inexplicable. Further investigations, 

 however, are needed to enable us to decide with certainty whether 

 the mode of explanation which has been indicated is admis- 

 sible. 



In connexion with the above, experiments were also made with 

 some Geissler's tubes, in order to ascertain whether the disjunc- 

 tion-current could be perceived in them or not. With three of 

 them, one (according to the label) containing oxygen, another hy- 

 drogen, and the third chlorine, distinct deflections were exhibited; 

 while another, which contained carbonic acid, as well as one with- 

 out label, gave no distinct proof of the existence of a disjunction- 

 current. 



4. The current in the voltaic luminous arc is well known 

 to occasion a greater disintegration of the positive than of the 

 negative pole. When two equal polai\ surfaces, between which 

 the discharge from an electrophorus machine has been for 

 some time taking place, are closely examined, it is easy to dis- 

 criminate the positive polar surface from the'negative; for the 

 former appears more altered than the latter. Hence positive 

 -electricity is most active in the disintegration. As positive elec- 

 tricity readily issues from a sharp point without producing 

 there a more powerful disintegration, it must follow that, when 

 one pole consists of a point and the other of a plane disk at 

 Tight angles to the plane of discharge, the disintegration is 

 greatest when the positive current goes from the disk to the 

 point. When, therefore, the discharge goes through the spark 

 from the disk to the point, it is to be expected that the disjunc- 

 tion-current will be stronger — partly because the electromotive 

 force of the disjunction increases with the disintegration, and 

 partly also because the quantity of particles detached from the 

 poles is greater, and therefore the conducting-power of the spark 

 is better. 



To test the accuracy of what has here been said, a round brass 

 disk 2*7 millims. in diameter was fastened on one of the two 

 metal rods of the glass cylinder, and upon the end of the other 

 rod a conically sharpened brass point was screwed. 



current traverses it in either direction ; and on this assumption I have based 

 a method of directly measuring the electromotive force of disjunction. 

 This assumption has been found to be incorrect. The spark undergoes a 

 considerable change by the passage of the voltaic current, so that the de- 

 terminations obtained can only be regarded as valid for the case in which a 

 voltaic current traverses the spark. 



