68 



SCIENCE 



[N. S. Vol. XXXVIII. No. 967 



effect when electrons are emitted by a conduc- 

 tor and a corresponding heating effect when 

 they are absorbed. Both these effects" have 

 since been detected experimentally and found 

 to be of the expected magnitude, within the 

 limits of experimental error. The magnitude 

 and distribution of energy of the emitted elec- 

 trons has been found by experiment to be that 

 given by Maxwell's law,' in accordance with 

 the requirements of the theory. Finally, the 

 same general train of ideas has led to valuable 

 applications in the direction of the theory of 

 metallic conductors," contact potential" and 

 photoelectric action.' 



It has long been known that ions are 

 emitted in a number of cases in which solids 

 react chemically with gases. The recent ex- 

 periments of Haber and Just' indicate that 

 the alkali metals liberate electrons when they 

 are attacked by certain gases. It seems likely, 

 from various considerations," that effects of 

 this nature would account for most of the 

 emission from heated sodium which was 

 measured by the writer." In consequence of 

 this conclusion, together with the results of a 

 number of experiments which are at first sight 

 in conflict with the theory referred to at the 

 beginning of this paper," the view appears to 

 have become rather prevalent that the emis- 

 sion of electrons from hot bodies is invariably 

 a secondary effect arising in some way from 



^Eiehardson and Cooke, Phil. Mag., Vol. 20, p. 

 173 (1910), Vol. 21, p. 404 (1911); Cooke and 

 Eiehardson, Phil. Mag., Vol. 25, p. 624 (1913). 



* Richardson and Brown, Phil. Mag., Vol. 16, 

 p. 353 (1908); Richardson, Phil. Mag., Vol. 16, 

 p. 890 (1908); Vol. 18, p. 681 (1909). 



Richardson, Phil. Mag., Vol. 23, p. S94 (1912) ; 

 Vol. 24, p. 737 (1912). 



"Richardson, Phil. Mag., Vol. 23, p. 263 (1912). 



'Richardson, Phil. Mag., Vol. 24, p. 570 (1912) ; 

 Richardson and Compton, Phil. Mag., Vol. 24, p. 

 575 (1912). 



'Ann. der Phys., Vol. 30, p. 411 (1909); Vol. 

 36, p. 308 (1911). 



" Cf. Tredenhagen, Verh. der Dewtsch. Physilc. 

 Ges., 14 Jahrg., p. 384 (1912) ; Richardson, Phil. 

 Mag., Vol. 24, p. 737 (1912). 



^"Phil. Trams., A, Vol. 201, p. 497 (1903). 



"Cf. Pring and Parker, Phil. Mag., Vol. 23, p. 

 192 (1912). 



traces of chemical action. That this view is 

 a mistaken one is, I think, conclusively shown 

 by the following experiments which I have 

 made with tungsten filaments. 



The tests to be described were made with 

 experimental tungsten lamps carrying a ver- 

 tical filament of ductile tungsten which passed 

 axially down a concentric cylindrical electrode 

 of copper gauze or foil. The tungsten fila- 

 ments were welded electrically in a hydrogen 

 atmosphere to stout metal leads. These in turn 

 were silver soldered to platinum wires sealed 

 into the glass container. The lead to the 

 copper electrode was sealed into the glass in 

 the same way. The lamps were exhausted with 

 a Gaede pump for several hours, during which 

 time they were maintained at a temperature 

 of 550-570° C. by means of a vacuum furnace. 

 The exhaustion was then completed by means 

 of liquid air and charcoal, the tungsten fila- 

 ment meanwhile being glowed out by means 

 of an electric current at over 2200° C. Most 

 of the tests were made after the furnace had 

 been opened up and the walls of the lamps al- 

 lowed to cool off. They were always consider- 

 ably above the temperature of the room on ac- 

 count of the heat radiated by the glowing fila- 

 ment. 



The processes described are extremely well 

 adapted for getting rid of the absorbed gases 

 and volatile impurities which form such a per- 

 sistent source of difficulties in experiments of 

 this character. Unless some such treatment 

 is resorted to, the metal electrodes and glass 

 walls of these tubes continue to give off rela- 

 tively large amounts of gas under the influ- 

 ence of the heat radiated from the filaments 

 and it has always been possible that this evo- 

 lution of gas might have played an important 

 part in the electronic emission. The mode of 

 treatment used, for which I am largely in- 

 debted to the experience and suggestions of 

 Dr. Irving Langmuir, of the General Electric 

 Company's Research Laboratory at Schenec- 

 tady, N. T., seems very superior to anything in 

 this direction which has previously been pub- 

 lished. 



Tests have been carried out covering the 

 alternative hyixitheses as to the possible mode 



