Some Contemporary Advances in Physics - VI Electricity in Gases

T HE physicists of a quarter of a century ago, who devoted themselves to the study of electricity in gases, were happily inspired; for among the myriad of intricate and obscure phenomena which they observed there are some few of an extreme simplicity, 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 deeper understanding of nature which is superseding the physics of the nineteenth century, and the physics of today is founded upon their efforts. The electron was perceived for the first time in the course of observations 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 discovery of the atom is commonly credited to the chemists; yet fifteen years have not passed since students of chemistry were being warned by a famous teacher that " a t o m " and "molecule" are figurative words, not on any account to be taken literally! The laws of chemical combination were held insufficient to prove that atoms have any real existence; though elements may always combine with one another in unchanging proportions, this does not prove anything about the weights of the atoms, or their sizes, or their qualities, 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 approach, and know what happens to them when they strike one another or are struck by electrons; now that we can fill in the picture of the atom with so many and so diverse details, we are indebted for this progress chiefly to the men who gathered the data and made the theories concerning the conduction of electricity in gases.