Some Contemporary Advances in Physics VI 

 Electricity in Gases 



By KARL K. DARROW 



1. Introduction 



Till-; i)li\>iii>ts of a (jiiarttT of a century ago, who dcvoti-d iIh-iii- 

 selves to the study of electricity in gases, were liappiK' inspireti; 

 for among the myriad of intricate and obscure phenomena which 

 the\- observed there are some few of an extreme sinijjlicity, in which 

 the qualities of the individual atoms of matter and electricity are 

 manifest; in analyzing these they entered upon the path that led most 

 directly to the dee[)er understanding of nature which is superseding 

 the physics of the nineteenth century, and the physics of today is 

 founded upon their efTorts. The electron was perceived for the first 

 time in the course of ol)ser\ations on the electric discharge in rarefied 

 gases, and other experiments in the same field established the atom 

 in science as a real and definite object. The disco\'ery of the atom 

 is commonly credited to the chemists; yet fifteen years have not passed 

 since students of cluinistr>- were being warned by a famous teacher 

 that "atom" and "molecule" are figurative words, not on any account 

 to be taken literally! The laws of chemical combination were held 

 insufficient to pro\-e that atoms ha\'e any real existence; though 

 elements nia\' always combine with one another in imclianging propor- 

 tions, this does not pro\e anytiiing about the weights of the atoms, or 

 their sizes, or their (|ualities, or even that all the atoms of an element 

 have the same weight, or even that there are any atoms at all. Now 

 that we are past the necessity for this caution, and can count atoms, 

 and measure their masses, and infer something about their structure, 

 and estimate how close together they can a|)proach, and know wliai 

 happens to them when they strike one another or are struck 1)\- 

 electrons; now that we can fill in the jiicture of the atom with so many 

 and so diverse details, we are indebted for this progress chiefly to the 

 men who gathered the daUi and made the theories concernini; the 

 conduction of electricity in gases. Many will remember how in ihc 

 years before the great war this field of research seemed the most vital 

 part of physics, the most inspired with a sense of new life and swift 

 advance; now others share with it the centre of the stage, but they 

 won tiieir places chiefly l)ecause of the light it shed upon them. 



It seems strange that the (low of electricity in gases should have 

 proved easier to interpret than the How of electricity in ntetals, which 

 in appearance is certainly b\ f,ir the sinijiler. One ai)plies tin- tcrniiiials 



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