THE DISCOVERY OF ELECTRON WAVES 



481 



a great part of the success of the definitive experiments is due, suc- 

 ceeded Dr. Kunsman in 1924. 



2 



1.5- 



0.5- 



EOUATION OF LINE ^ = 

 1^ '">' 2 300 



7^ = ,J10.y/2xi0-» cm 



12 25 



ELECTRON WAVE-LENGTH5 



FROM 

 PLANE GRATING FORMULA 

 1/ V- 



vs.y;/2 



FROM OBSERVATIONS WITH 

 DIFFRACTION APPARATUS. 



SAME - PARTICULARLY RELIABLE 



SAME -GRAZING BEAMS. 



FROM OBSERVATIONS WITH 

 REFLECTION APPARATUS 



/v 



1/ /z 

 'V 



Fig. 4 — Test of the de Broglie formula X = hip = h/mv. Wave-length computed 

 from diffraction data plotted against 1/F"^ ( V, primary beam voltage). For precise 

 verification of the formula all points should fall on the line X = 12.25/ F^'^ plotted in 

 the diagram. 



I would Hke also at this time to express my admiration of the late 

 Dr. H. D. Arnold, then Director of Research in the Bell Telephone 

 Laboratories, and of Dr. W. Wilson, my immediate superior, who were 

 sufficiently far-sighted to see in these researches a contribution to the 

 science of communication. Their vision was, in fact, accurate for 

 today in ours, as in other industrial laboratories, electron diffraction is 

 applied with great power and efficacy for discerning the structures of 

 materials. 



But neither of this nor of the many beautiful and important re- 

 searches which have been made in electron diffraction in laboratories 

 in all parts of the world since 1927 will I speak today. I will take time 

 only to express my admiration of the beautiful experiments— differing 

 from ours in every respect — by which Thomson in far-away Aberdeen 

 also demonstrated electron diffraction and verified de Broglie's 

 formula at the same time as we in New York. And to mention, as 



