Disjunction-currents between Poles of different shapes. 31 



gradually rarefied. But the deflection is not caused during the 

 whole time by the same current : in the unrarefied air the direc- 

 tion of the deflection is chiefly determined by the disjunction- 

 current, and in the rarefied air by the second induction-current. 

 If, on the contrary, the valve is applied, so that the first induc- 

 tion-current goes from the disk to the point, this current acquires 

 the upper hand and determines the direction of the discharge 

 when the air is rarefied; hence in this case the deflection 

 must alter its direction when the air is gradually rarefied. In 

 the space filled with air the disjunction-current has the upper 

 hand ; in rarefied air the first induction-current is the more 

 powerful. 



By the foregoing investigations we have obtained a simple 

 means of experimentally proving whether a given deflection of 

 the magnetic needle is caused by a disjunction- or by an in- 

 duction-current. Experiments 22 to 24 show that when the 

 spark is formed between the disk and the point, the disjunction- 

 current is most powerful when the discharge goes from the disk 

 to the point, or, what is the same thing, when the disjunction- 

 current goes from the point to the disk. Experiments 27 

 and 28, on the contrary, have shown that when an induction- 

 current produces a deflection, this is greatest when the induc- 

 tion-current goes from the disk to the point. If, therefore, 

 the current which produces the deflection first goes from the 

 disk to the point, and thereupon by reversing the valve a greater 

 deflection is obtained, it is a case of a disjunction- current ; but 

 if the deflection is smaller when the valve is reversed, an in- 

 duction-current is the cause. This holds, without exception, 

 when the deflection is produced either by a disjunction- or by 

 nn induction-current only. When both currents act simulta- 

 neously and to the same extent, this rule, as may be easily 

 seen, may, under certain circumstances, be misleading. 



M. Biess has already found that, when the valve was full of 

 air, the greatest deflection was obtained when the second induc- 

 tion-current (which, in his opinion, determines the direction of 

 the deflection) went from the point to the disk. This, however, 

 as we have seen, is a proof that the deflection was caused by a 

 disjunction-current. 



The subsequent series of experiments confirm this observa- 

 tion, and prove afresh that the deflection in the case in question 

 was caused by a disjunction-current. The expression "Disk 

 positive," signifies that the second induction-current went from 

 the disk to the point ; and the expression the " Disk negative ;; 

 signifies the contrary. 



