THE ELECTRON— COMPTON 221 



chemical elements like our sun. But in 1922, a young Indian physicist, 

 Meghnad Saha, first applied atomic structure theory and knowledge of 

 ionizing potentials to the sun and stars. He considered ionization in 

 the hot vapors of the stars to be like a chemical dissociation produced 

 by heat, in which the products of dissociation are electrons and the 

 positive ionic residues of the atoms, and in which the heats of dis- 

 sociation are given by the ionizing potentials of the atoms. In this 

 way was developed a rational quantitative interpretation of stellar 

 spectra which has thrown enormous Ught on the problem of conditions 

 of temperature, pressure and condition of the chemical elements in 

 stars. RusseU in America and Milne in England have ably applied and 

 extended this theory. 



THE ELECTRON IN INDUSTRY 



Finally, I come to the last phase of my subject, the social signifi- 

 cance of the electron. By this I mean, of course, its useful applica- 

 tions. The first of these was Edison's invention of a thermionic rec- 

 tifier, based on his discovery that negative electricity would flow 

 across a vacuum from a hot filament to an adjacent electrode, but 

 would not flow in the opposite direction. This was some years before 

 the electron was discovered as the responsible agent in this phenom- 

 enon. But within a few years after the discovery of the electron, 

 Fleming had shown that this same device will operate to rectify 

 radio wave impulses, and thus permit their detection with a sensi- 

 tive direct-current instrument. From this was patented the Fleming 

 valve. 



Once the basic character of thermionic emission was understood, 

 and spurred on by the opportunities opening up in the radio field, 

 new inventions, improvements, and applications of thermionic devices 

 came rapidly. Of major importance was the three-electrode tube am- 

 plifier of De Forest. Industrial research laboratories in the com- 

 munications and electric manufacturing business took the lead in 

 developing techniques and in penetrating scientific exploration. Note- 

 worthy were the vacuum techniques and the monomolecular layers of 

 activating materials developed by Langmuir and the high-vacuum 

 thermionic X-ray tube of Coolidge. In the Bell Laboratories, oxide- 

 coated filament tubes of good performance were developed and applied 

 particularly to use in long-distance telephony. Let me give just two 

 illustrations of the marvelous powers of some of these instruments. 



It has been calculated that the energy of a trans-Atlantic radio 

 signal caught by the receiving station in Newfoundland comes in at 

 about the rate required to lift a fly 7 inches in a year. 



What is the largest number that has any physical significance? 

 This is impossible to answer, being largely a matter of definition. 

 But one common answer to this is 10"°, or one followed by 110 



