and Ohmic Resistance of Gases. 353 



does not indicate the fall of potential through the small 

 resistance of the tube during the instant when the discharge 

 passes, but maintains an indication of a high difference of 

 potential. 



In order to apply systematically this new method of 

 measuring resistances, our next step was to prepare a series 



Fig. 1. 



B, battery of 5000 to 10,000 storage cells. 



C, condenser of 1000 to 18,000 electrostatic units. 

 K, small resistance to damp oscillations. 



S, spark-gap between cadmium terminals. 



T, Pliicker tube containing gas. 



W, chief water resistance of 5 to 50 megohms. 



of standards — photographs of the oscillatory sparks of con- 

 densers of different sizes, damped by known resistances 

 which were substituted for the Geissler tube in the condenser 

 circuit. In all these experiments, of course, the small 

 resistance on the left-hand side of the sketch was cut out by 

 a suitable key. Three large ley den-jars, each 30 cm. in 

 diameter and 50 cm. high, having a capacity of 6000 electro- 

 static units apiece, were used either singly or together to act 

 as the condenser ; the waves generated by these large 

 capacities were much too long to interfere with one another 

 upon so short a circuit. The resistances were wires of manganin 

 01 mm. in diameter, stretched on both sides of long strips 

 of thin vulcanite plate, the idea of this arrangement being to 

 eliminate self-induction and yet to prevent the short-circuiting 

 of the high potential. The spark-gap usually consisted of 

 cadmium terminals arranged in the focus of a revolving 



