298 Mr. J. Frenkel on the Surface Electric 



w by the relation eV = w, where e is the electronic charge. 

 This quantity V may be called the intrinsic potential of the 

 body. The difference between the intrinsic potentials of two 

 metals must be equal to their contact electromotive force 

 (neglect being made of the Peltier effect) ; a fact which has 

 been verified in a few cases by comparison of the theoretical 

 values, obtained from thermionic data, with those directly 

 measured by the electrostatic method. It may be mentioned 

 here that the intrinsic potentials of different metals, as 

 calculated from Richardson's formula, remain in rather 

 narrow limits and amount to a few volts (4*48 volts for 

 Tungsten)*. 



It is well known that metals are not sensitive to light of 

 any wave-length ; the photo-electric emission begins when 

 the frequency v of the exciting light exceeds a certain 

 •critical value v , the kinetic energy of the ejected electrons 

 \mv 2 being connected with v by Einstein's formula 

 ±mv 2 = h(v — vq), where h is Planck's constant. The remark- 

 able exactitude of this formula has been conclusively proved 

 by the recent experiments of Millikan f, who also showed 

 that the difference between the values of hv for Na and Li 

 was just equal to their contact electromotive force (multiplied 

 by e), as measured by the Kelvin method. In Einstein's 

 formula hv corresponds to w in that of iiiehardson, being 

 equal to the energy lost by the electron on its way through 

 the electric double-layer enveloping the metallic surface. 

 The intrinsic potentials, calculated from the relation Ve = hv , 

 are equal to 1*81 volts for Na and 2*24 volts for Li J. 



The existence ot electric double-layers on the surface of 

 metals is thus beyond doubt, and the question arises as to 

 their origin. 



§ 2. The old view, which was in favour of an external 

 origin depending upon occluded gases, chemical action, &c, 

 is now being supplanted by the opposite view, which, leaving 

 to the external agencies but a secondary role, tends to trace 

 the origin of intrinsic potentials to the action of some intrinsic 

 cause, more appropriate for the explanation of their com- 

 parative constancy. It is the main purpose of this paper to 

 show that such a cause really exists ; its extreme simplicity 

 is, perhaps, the only reason why it has not been noticed 

 until now. 



Let us imagine a metallic body absolutely cleaned from 

 alien substances and placed in vacuo. It is composed of 

 identical atoms packed rather closely together. Every atom 



* H. Lester, Phil. Mag. March 1916. 



t Phys. Rev. March 1916. 



J The respective values of v Q are 439 X 10 13 and 57 X 10 13 . 



