2 Duane — Emission of Electricity. 



appeared in Science.* Since then I have been able to repeat 

 the experiments and carry the investigation somewhat further 

 in the radium laboratory of the University of Paris. It gives 

 me very great pleasure to thank Madame Curie and her assist- 

 ants for their kindness to me during my researches. 



2. Figure 1 represents the arrangement of the apparatus. 

 J. is a metallic cylindrical electrode, ll mm long and 3'42 mm in 

 diameter, made radio-active by exposure to radium emanation. 

 B is a tube of the same material as A, having an internal 

 diameter of 4'30 mni . A can be held accuratelyin a position 

 coaxial with B by the two metal points aa, and in this position 

 there is everywhere a distance of only -44 nim between the outer 

 surface of A and the inner surface of B. The two metal 

 points aa are imbedded in ebonite plugs, the upper point being 

 completely insulated by the ebonite (in some experiments it 

 formed one piece with A), and the lower one connected by 

 suitably protected wires to a quadrant electrometer. The cur- 

 rents of electricity flowing toward or away from A were meas- 

 ured sometimes by the rate of change of the deflection of the 

 electrometer, and sometimes with the aid of a piezo-electric 

 quartz. The metal rings ho, connected to earth, served as guard 

 rings to prevent currents from flowing between A and B along 

 the surface of the ebonite. 



3. The method of procedure was as follows : The elec- 

 trode A was suspended by a pair of metal tweezers in radium 

 emanation contained in a metal can for a period of at least 20 

 hours. It was charged during the period to a negative poten- 

 tial of 88 volts with respect to the can, thus insuring approxi- 

 mately saturation amounts of the induced activity. At the 

 end of the period A and the ebonite plug were quickly placed 

 in their positions in the tube B, and hot sealing wax poured into 

 the cup C so as to form an air-tight joint between the plug 

 and the tube. The air between A and B was then quickly 

 exhausted. In the earlier experiments it was pumped out to a 

 pressure of 1 or 2 mm of mercury by means of a mechani- 

 cal oil pump, and then the residual air allowed to expand 

 quickly into a glass globe previously exhausted to a good 

 vacuum. In the later experiments, however, the exhaustion 

 was accomplished by means of carbon cooled to the tempera- 

 ture of liquid air, the well-known Dewar method. After the 

 vacuum had been produced the current flowing to or from A 

 was measured at intervals of from two to Ave minutes, the 

 tube B being at zero potential or charged by a battery posi- 

 tively or .negatively. Usually the first satisfactory reading 

 could be taken ten or twelve minutes after the electrode A 

 had been withdrawn from the emanation. 



* Science, xxiv, pp. 48-49, 1906. 



