272 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



A water-cooled gap as shown in Figure 2 was, however, used through- 

 out this investigation. By reference to the drawing this gap is seen 

 to consist of two hollow threaded electrodes capped with aluminum 

 and copper, respectively, and each provided at the outside end with 

 an inlet and outlet tube for the passage of the cooling water. The 

 terminals are enclosed in a hard rubber casing provided with a circular 



p/wvyw 



L 







<I) — Tmn^ 



L-0-1 



Figure 3. Diagram of Comiections. 



glass front. Hard rubber disks attached to the electrodes serve for 

 adjusting handles. The figure is a reduction in the ratio of 5 to 2. 



The general diagram of connections is shown in Figure 3. >S' is a 

 source of direct current of a few hundred volts, and, in what follows, 

 530 is to be assumed unless otherwise stated. lo is a D. C. ammeter 

 which measures the current in the supply circuit. This circuit also 

 contains the two inductances or choke coils Lo Lo, and a variable re- 

 sistance 7?o, capable of reducing the current to about 0.2 ampere. In 

 the following experiments Lo Lo are ordinary A. C. arc-light induct- 

 ances, and Ro is a resistance, adjustable in one half ampere steps, in 

 series with a variable copper-sulphate electrolytic resistance. Cx and 

 C-i. are variable air condensers, G the gap, L^ and L^ the variable 

 primary and secondary of the closely-coupled oscillation transformer, 

 and 1.2 a hot-wire ammeter. 



(2) Operation of Gap. 



The system will start automatically if the distance between the 

 terminals is not much greater than 0. 1 mm. In appearance the dis- 

 charge resembles a very minute arc, of an intense reddish-purple color, 

 absolutely quiet and stationary. The discharge remains at one point 

 on the electrodes for several minutes until the aluminum is slightly 

 pitted, when it suddenly shifts to another point. When the discharge 

 is examined by means of a spectroscope only the primary hydrogen 



