322 M. P. Riess on the Passage of Electric Currents 



by pushing the bundle of iron wires further into the primary 

 coil, in order that the current might traverse the space between 

 the electrodes. In both positions of the electrodes the deflection 

 was normal, but it was greater with the knob negative than 

 positive. A smaller knob, Jr^th of an inch in diameter, was 

 placed at a distance of y^ths of an inch from the small surface 

 in the cover. When the knob was negative, the deflection 

 amounted to 60^ and was normal; when positive, the deflection 

 was zero at the moment of closing the circuit, but passed into a 

 normal or an abnormal one of 10^. The knob was replaced by 

 a horizontal brass disc, yiths of an inch in diameter and 1^ inch 

 distant from the platinum surface. The disc being negative, the 

 deflection was normal, and attained the maximum ; when posi- 

 tive, it was abnormal, and amounted to 20°. I varied these ex- 

 periments in numerous ways, but the common result of all was, 

 that when the small platinum surface was positive, the deflection 

 of the needle was always normal, and always occurred imme- 

 diately after closing the induction circuit ; when, on the contrary, 

 that surface was negative, the deflection was sluggish and retro- 

 grade. That in the last case the deflection is sometimes ab- 

 normal, has been observed also by JNI. Gaugain, who. Lad he 

 taken the observation suflSciently into consideration, would not 

 have been led to the erroneous conclusion which he has drawn 

 from his experiments. For there are undoubtedly two oppositely 

 directed induction currents acting in these experiments : the 

 interruption current, in reference to which the poles of the in- 

 duction coil have been defined ; and the contact current, in refer- 

 ence to which the names of the poles of the induction coil must 

 be changed. The action of the two opposite currents can be 

 demonstrated by means of a decomposing apparatus still more 

 successfully than by tiie galvanometer. Besides the galvano- 

 meter and the cylinder of rarefied air, in which a knob was placed 

 l^ths of an inch from the small surface, two platinum points were 

 introduced into the induction circuit ; they were about one inch 

 asunder, and stood on a piece of paper moistened with iodide of 

 potassium. As before, the commutator changed the direction 

 of the induction current in the glass cylinder alone. When the 

 small surface in the cylinder was connected with the positive 

 pole of the induction coil, the stain of iodine in seven successive 

 experiments appeared only under that platinum point which was 

 positive in reference to the interruption current ; when, on the 

 contrary, the surface was in communication with the negative 

 pole, the stain of iodine in thirteen experiments appeared eight 

 times under the other platinum point alone, and five times under 

 both points. The knob in the cylinder was next placed ly\ 

 inch distant from the small surface : when the latter was posi- 



