The pressure upon the poles of metallic and composite arcs, including an enquiry into the reactions consequent upon electron emission

Experiments upon the pressure experienced by the poles of a carbon arc led to the theory, which was put forward tentatively, that it was due to the recoil consequent upon the projection of electrons from the poles. Experiments have subsequently been made upon metallic arcs, using poles of iron, silver, copper, and an alloy of silver and copper, and also upon a composite arc in which one pole was of silver and the other of carbon. In dealing with the carbon arc it was found possible to eliminate the effects of the electromagnetic influence of the rest of the circuit and of the earth’s magnetic field, by employing what was called the double-arc method; but in the present set of experiments the rapid melting of the metal rods made it expedient in the majority of cases to employ the less direct single-arc method, which had also been used in the carbon investigation, the necessary allowances for the disturbing influences being made in the manner already described. In the case of the copper arc a satisfactory series was also obtained by using the two arcs.