48 Dr. Foote and Dr. Mohler on Ionization and 



The writers believe that the above method of determining 

 li is capable of much higher accuracy than the photoelectric 

 method if developed to the degree of refinement which the 

 latter method has received. For very high precision a source 

 of electrons possessing a uniform velocity is desired. This 

 can be realized by magnetic separation similar to the method 

 recently employed by Richardson and Bazzoni *, or it can be 

 accomplished by the use of a properly arranged electric field. 

 Dr. Tate suggested a year ago the great value to be derived 

 from such an experimental procedure. The writers contem- 

 plate using in the near future a uni velocity stream of elec- 

 trons in mercury vapour. Inasmuch as the present deter- 

 mination of h is by an entirely new method, it is of interest 

 to compare determinations by other methods. The following 

 table presents a summary statement of recent data : — 



Table VII. 



Determination of A. 



Method. Observer. h . 10 27 . 



Black body radiation. Ooblentz. 6*56 erg sec. 



X-rays. Blake and Duane. 6*56 



Photoelectric effect. Millikan. 657 



Ionization and Resonance Foote and Mohler. 6*55 

 Potentials. 



In a recent paper Sanford f has developed a theory of 

 the relation between ionizing potentials and atomic charges. 

 The writers are unable to reconcile this theory with the 

 Einstein equation or with experimental data. Sanford pro- 

 poses the following relations : — 



(1) Nuclear charge =Q = 2*95 . 10" 12 / ^X where X is the 

 wave-length of the radiation emitted. 



(2) Ionization potential = V = (Q-2*42) 1*4, whence 



(3) V = 412 / s/X — 339 for X expressed in Angstrom 

 units. On multiplying (3) by e, the equation takes the 

 following form : — 



(4) eY = a vV— ft whereas the quantum relation which 

 is known to be correct (see fig. 4 as one example of its 

 verification) is given by eq. (5). 



(5) eY=hv. 



It is evident that Sanford' s equation (4) is incompatible 

 with the quantum relation (5). 



* Phil. Mag. xxxiv. p. 285 (1917). 

 t Phys. R. ix. p. 575 (1917). 



