Electric Forces and Quanta

Abstract

IT is just about twenty-five years since Lord Kelvin spoke of “two clouds” obscuring “the beauty and clearness of the dynamical theory which asserts light and heat to be two modes of motion.” The clouds which Lord Kelvin saw as clouds no bigger than a man's hand have grown until they have almost filled the firmament: little can now be seen of the beauty and clearness of the dynamical theory of which Lord Kelvin spoke. The old dynamical theory has given place to the new theories of relativity and of quanta; what Lord Kelvin thought were transient clouds shortly to melt away have proved to be new theories in process of growth; “the beauty and clearness” he saw under these clouds was mostly a mirage.