Disjunction-currents hetween Poles of different shapes. 29 



This last experiment therefore confirms the preceding. Hence 

 it cannot be the induction-current opposite in direction to the 

 discharge which most readily traverses the spark, but must be 

 the other. 



As it is now certain that the induction-current which has the 

 same direction as the discharge most readily traverses the spark, 

 another conclusion can be drawn from the preceding experiments ; 

 for they show that the diminution in the deflection of the magnetic 

 needle which the induction-current causes is greater when that 

 current traverses the spark from the disk to the point than when 

 its direction is opposite. An induction- current which traverses 

 a spark does so most readily when it can go from the disk to 

 the point. This result, which holds for the case in which the 

 spark passes in a space filled with air, is essentially the same as 

 that which Professor Riess found for the spark in rarefied air. 



6. We now proceed to the case in which the electrical dis- 

 charge traverses a spiral, and thereby produces induction in an 

 adjacent spiral. -When the latter spiral is connected with a gal- 

 vanometer and its ends are in metallic connexion, no deflection 

 is obtained, because the two induction-currents are equal and in 

 opposite directions. If, on the contrary, the spiral is opened so 

 wide that formation of sparks takes place, the magnetic needle 

 makes a deflection which indicates that the inducing current is 

 in the same direction as the discharge-current. When the spark 

 is formed in a space containing air, this holds, under ordinary 

 circumstances, whatever be the shape of the poles. We really 

 have not less than four currents — that is, two induction-currents 

 and two disjunction- currents. When the galvanometer is in- 

 serted in the conduction and not provided with a suitable bridge, 

 the system of currents is still more complex. Both induction- 

 currents have the same electromotive force; and if the spark 

 opposed the same resistance to each, there would be no action 

 upon the galvanometer. As regards the disjunction-currents, 

 their electromotive forces can by no means be equal. The 

 first induction-current, or that which is in the opposite di- 

 rection to the discharge, must break through a dense layer of air ; 

 and as this cannot occur without a more considerable tension of 

 the electricity, a powerful disintegration of the polar surfaces 

 thereby ensues. The second induction-current, or that which 

 goes in the same direction as the discharge, instantaneously 

 follows the first, strikes therefore, in the spark, air already 

 rarefied, and the disintegration is less. On this account the first 

 induction-current must produce the most powerful disjunction- 

 current. This latter current, which goes in the same direction 

 as the second induction-current, produces the deflection of the 

 magnetic needle. Hence the capacity of the first induction-cur- 



