Prof. 0. W. Richardson on Tltermlonics. 813 



The agreement between the various sets is not better than 

 it was before. For the other gases the values of c and C are 

 unknown as the viscosities have not been measured. 



Happel (Ann. d. Pliys. xxi. p. 312, 1906) has calculated 

 the values of b for A, Kr, and X from Boltzmann's modified 

 form of van der Waals' equation. His results are given 

 in c.c. per 1 g. Reduced to unit- volume thev are for 

 A &h=0-00214, Kr & H =0-00283, and X 6 H = 0-00370. 



These values are greater than those calculated above from 

 the original van der Waals' equation, and give for a calcu- 



IT 



lated from V= -, No- 3 the following- results : — 



b ° 



Kr. 



crxlO*cm. '[ 3-36 3 69 402 



The agreement between b and §(/* — 1) (Cf. Part I. § C2d) 

 is now worse than before. Happel thinks, therefore, that 

 either the Clausius-Mosotti relation or the Maxwell relation 

 cannot hold for these gases. For He, at any rate, the latter 

 seems to hold; the dielectric constants of the other gases are, 

 however, unknown, so that for the present the discrepancy 

 cannot be explained away. 



To Part II. — Using Happens value of b for Argon, N 

 comes out to 1*08 x 10 1<J . I have also tried the effect of 

 introducing Reinganum's correction on the values of N. 

 Taking the values of V from /x as these are more comparable 

 than those from b, we get for He N = 13*2 x 10 19 , and for 

 A N = 2'7xl0 19 . The latter value agrees well with the 

 theoretical — 2*75 X 10 19 , but the agreement is probably only 

 a chance one. 



LXXV1I. Thermionic*. By 0. W. Richardson, M.A., 

 D,Sc, Professor of Physics, Princeton University *. 



§ 1. ~VT/"HILE fully alive to the desirability of restraining 

 H as much as possible the ever-increasing growth 

 of our scientific nomenclature, the author has felt for some 

 time that there is real need of a single word to denote the 

 branch of phvsics which is alluded to in the literature with 

 varying dignity as "the emission of ions by hot bodies/' 

 " the leak from hot wires," and a number of other phrase.-. 

 After giving the matter due consideration, the author 

 * Communicated by the Author. 



