For five years (1865-1870) he lived a retired life at Glenlair, broken by visits to London, Cambridge, Edinburgh, and the Continent. But it was then that he found leisure to complete the great work of his life the Treatise on Electricity and Magnetism, published in two volumes in 1873. The aim of the work is to give a connected and thorough mathematical theory of all the phenomena of electricity and magnetism. He started from the facts observed in Faraday's experiments, and in their light he read the old theory of electric action. This work has served as the starting point of many of the advances made in recent years. Maxwell is the scientific ancestor of Hertz, Hertz of Marconi and all other workers at wireless telegraphy. In the introductory chapter Maxwell remarks that the Earth (which was made the basis of the metric system) is not sufficiently constant either in form or in period of rotation; and advises physicists who may judge their papers worthy of a greater endurance to base their units upon the wave-length and period of some specified molecule. Humor or not, Michelson in this country has actually compared the meter of the archives with the wave-length of a certain ray of light.
Professor Tait gave Maxwell much assistance in the preparation of his great Treatise. He urged him to introduce the Quaternion method; but Maxwell found serious practical difficulties. For one thing Hamilton makes use of the Greek alphabet, and Maxwell found that all the Greek letters had already been appropriated to denote physical quantities. But Maxwell was an intuitionalist, and he never trusted to analysis beyond what he could picture clearly. So he adopted the rather curious middle course. "I am convinced that the introduction of the ideas, as distinguished from the operations and methods of Quaternions, will be of great use to us in all parts of our subject." In this departure we have the origin of the school of vector-analysts as opposed to the pure quaternionists.
In 1870 the Duke of Devonshire, who was Chancellor of the University of Cambridge, signified his desire to build and equip a physical laboratory. The Senate accepted the gift,
