CONTEMPORARY ADVANCES IN PHYSICS 109 



W 1.007775 ± .000035 C^^ 12.0036 ± .0004 



*H2 2.01363 ± .00008 N" 14.008 ± .001 



He4 4.00216 ± .00013 O^^ 16.0000 (standard) 



*Li« 6.0145 ± .0003 F^^ 19.000 ± .002 



*Lr 7.0146 db .0006 * Ne^o 19.9967 ± .0009 



*Be' 9.0155 ± .0006 * Ne^^ 21.99473 ± .00088 



Bi" 10.0135 ± .0005 *CF5 34.9796 ± .0012 



B" 11.0110 ± .0005 *CF 36.9777 ±'.0019 



The table of the chemical atomic weights reproduced in the First 

 Part has suffered two alterations: a very slight change in the given 

 value for K, from 39.10 to 39.096; and an important change in the 

 chemical atomic weight of carbon, which rises from 12.00 to 12.011, 

 and now permits of an abundance of C^^ easier to reconcile with the 

 observed intensities of the spectrum-lines of this substance than was 

 the abundance, or rather the scarcity, implied by the former value.^ 



The list of isotopes detected by Aston 's mass-spectrograph has been 

 enlarged by the following examples,^ which the reader may enter upon 

 Fig. 6 of Part I: neodymium, Z = 60, A-Z = 83; samarium, Z = 62, 

 A-Z = 85, 86, 87, 90, 92; europium, Z = 63, A-Z = 88, 90; gadolin- 

 ium, Z = 64, A-Z = 91, 92, 93, 94, 96; terbium, Z = 65, A-Z = 94. 



New Developments in Transmutation: The Apparatus 



In the two years and a quarter which are all that have elapsed 

 since I published in this Journal an article on transmutation,^ the 

 situation in this field has vastly changed, and the prospects for the 

 future have been amplified immensely. So lately as the early spring 

 of 1932, disintegration of a nucleus had not yet been demonstrably 

 achieved except by alpha-particles possessing energy not smaller than 

 three millions of electron-volts. Schemes for producing five- and ten- 

 million-volt ions were already under way, being ardently pushed 

 onward because it was supposed that transmutation would never be 

 effected by any agency much feebler. But in the course of 1930, 

 Cockcroft and Walton of the Cavendish Laboratory had been em- 

 boldened by a theory (I will describe it later) to imagine that protons 

 of only a few hundred thousand electron-volts might be able to 

 transmute, and to risk their time and labors in the task of developing 

 powerful streams of such particles. After two years of work they 



' See an item in Nature, 132, 790-791 (Nov. 18, 1933). In the table of masses on 

 p. 303 of the First Part, change 1.0078 to 1.0072 and 4.002 to 4.001 (the former 

 values refer to complete atoms, not bare nuclei). 



* F. W. Aston, Nature 132, 930-931 (Dec. 16, 1933). 



^ "Contemporary Advances in Physics XXII," Bell System Technical Jotirnal, 10, 

 628-665 (October 1931). I refer to this article hereinafter as Transmutation. 



