710 



Dr. S. R. Milner on the Current-Potential 



adopted is shown diagrammatically in fig. 1. The pri- 

 maries of two induction-coils A and B and an automatic 

 mercury-break C are connected in series, so that both coils 

 are operated simultaneously by the break. At each break the 

 coil A sends a volley of rays from the cathode D of the 

 vacuum-tube V, and of these a narrow pencil, cut off by two 



metal screens E forming the anode and containing holes 

 1 mm. diameter, falls on the screen Fand gives a bright spot 

 of light. F is formed of powdered willemite on a glass 

 plate, sealing-waxed to the end of the tube. The coil B 

 simultaneously charges up a battery of leyden-jars until a 

 spark occurs across the gap Gr H between spherical brass 

 electrodes. The discharge current passes through inductance 

 coils L 1? L 2 ; L x is arranged so that the magnetic field of the 

 current deviates the cathode rays in a vertical plane, and 

 the two plates X and Y in the tube so that an electric field 

 between them gives a horizontal deviation. X, G, and E 

 are permanently connected to earth; Y may be connected to 

 any part of the discharge circuit H I J, or to one end of a 

 battery of small storage-cells the other end of which is to 

 earth, as desired. The whole tube from E to F, except the 

 part of it facing the coil L 1? is covered with tinfoil to avoid 

 the effects of stray electric fields. 



When Y is connected to the inner coating J of the jars, 

 the figure on the screen shows the spark current as ordinate 

 plotted against the p.d. between the coatings throughout 

 the whole period during which the rays caused by a single 



