524 TATE AND FOOTE : RESONANCE POTENTIALS 



(3) The experimental results of the present paper afford an- 

 other instance of the fundamental correctness of deductions 

 based upon Bohr's theory of atomic structures. 



In a very interesting paper 14 which has appeared since this 

 paper was written, Wood and Okano observe an emission of the 

 D lines at a potential of 0.5 volts, and the appearance of the 

 subordinate series (probably indicating ionization of the sodium 

 vapor) at 2.3 volts. These values are much lower than those 

 to be expected from the results of the present paper. It will be 

 remembered that Hebb ]5 has observed correspondingly low 

 values for the potentials necessary to excite the single-lined and 

 many-lined spectrum of mercury. The writers have observed a 

 similar phenomenon in connection with a determination, which 

 has just been completed, of the critical potentials for electrons 

 in potassium vapor. It was found that the first resonance 

 collision occurred at an effective applied potential of 0.2 volt 

 (correcting for the potential drop along the hot wire). In all 

 cases, however, the second resonance collision took place at a 

 potential 1.60 volts higher than the first. This value (1.60 

 volts) is exactly that required, on the basis of Bohr's theory, 

 to produce an emission of the fundamental lines (X = 7701.92 A 



o 



and X = 7668.54 A) of the principal series of the potassium 

 spectrum. Ionization of the potassium vapor was observed to 

 take place at a potential roughly one volt higher than the second 

 inelastic collision, i.e., at an effective potential of 3.2 volts + 1 

 volt, or 4.2 volts approximately. The theoretical value using the 

 limiting frequency of the principal series of potassium is 4.33 

 volts. 



It appears evident, therefore, that the electrons involved in 

 producing these effects have initial velocities of about 1.4 volts — 

 a value much greater than that to be expected. The reason for 

 these high initial velocities is difficult to find. The presence of 

 vapor or of a lime coating on the cathode seems necessary for 

 their production, and it is not impossible that chemical forces 



14 Wood and Okano. Phil. Mag., 34: 177. 1917. 

 16 Hebb. Phys. Rev., 9: .371. 1917. 



