Natural science in every department developed very wonderfully from its experimental side during the first half of the nineteenth century. Facts and observations accumulated to such an amount that, shortly after the middle of the century, there was felt the need of a great mathematical genius to bring the results of experiment into their proper places in the great body of applied and theoretic science. Nearly always such a demand meets with adequate response in its own due time. Clerk Maxwell came at this most opportune moment for science. No mathematical problem was too abstruse or difficult for him, and whatever he took up seriously he always illuminated, and usually solved its problems as completely as can be hoped for in the present state of scientific knowledge. It was particularly in electricity that his mathematical faculty proved of the greatest value, and that he found the abundant opportunities of which he knew so well how to take advantage. [Illustration: JAMES CLERK MAXWELL] Clerk Maxwell's theory of electricity, as developed in his classic treatise on "Electricity and Magnetism," is well called by Prof. Peter Guthrie Tait, "One of the most splendid monuments ever raised by the genius of a single individual." This book became the guide and companion of more physical scientists during the nineteenth century than perhaps any other written in that period. It was not alone in England or in English-speaking countries that it was accepted as an authority and constantly referred to, but everywhere throughout the world of science. Not to know it, was to argue that a man knew nothing of the profounder truths of electrical science and was only a seeker after superficial information. Clerk Maxwell was known and esteemed by all the great physical scientists of the world. His name is less widely known than that of most of the great discoverers in electricity, because mathematical achievement always has less popular attraction; but he deserves to be known by all who are interested in science, not only because of his magnificent contributions to mathematical electricity, but quite as much for qualities of heart and mind that stamp him as one of the very great men of the century so rapidly receding from us.