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 fertilisers, and was a pioneer in the use of nitrate of soda. After 1876 he left the entire management of the land to his younger brother, Edward Strutt.

This period saw the commencement of Rayleigh's lifelong interest in psychical research. At first he expected that investigation would rapidly lead to a definite conclusion, either positive or negative. Apparently he expected the former, in which case, his son believes, he was prepared to throw the greater part of his energies into a study of psychic phenomena. When it became clear that no such definite conclusion was being attained, he returned to orthodox scientific work. His recreations at this time were travel, tennis, and photography; a taste for music he shared with his wife. Shooting parties, which for some years he gave every winter, and ordinary social engagements, occupied but a small part of his time; it was not until later years that Terling became a gathering place for scientists from all the corners of the earth. He held strong conservative, and still stronger unionist, opinions, but the possibility of a political career did not attract him. He seconded the address in the House of Lords in 1875, and on rare occasions intervened in debate, but in general was resolute in not allowing politics to interfere with science.

Although he had taken his degree in 1865, and had immediately afterwards embarked on the experimental study of chemistry, it was not until 1869 that Rayleigh's first scientific paper appeared, bearing the title Some Electro-magnetic Phenomena considered in connexion with the Dynamical Theory. The paper has an interest beyond that which generally attaches to the first efforts of even the most brilliant investigators, in that it was a perfect example of the method its author was to pursue throughout his career. A dynamical theory of the electro-magnetic field had been given by James Clerk-Maxwell [q.v.] in terms of abstruse mathematical equations. Rayleigh elucidated and simplified this recondite theory—almost, one might say, made it intelligible to the average man—by showing that the intricate processes of the electro-magnetic field found practically perfect analogies in such well-understood phenomena as the bursting of a water-pipe under sudden pressure and the action of a hydraulic ram. The capacity for understanding everything just a little more deeply than anyone else, and the consequent capacity for exhibiting it in its simplest aspect, which formed so marked a characteristic of all Rayleigh's writings, was fully apparent in this, his first paper, which, as Sir Arthur Schuster remarks, ‘bears the imprint of the craftsman marked as clearly as a picture by Perugino carries the signature of the artist in every square inch’. From now until his death the 446 papers which are reprinted in the six volumes of his collected works issued in a steady, unbroken flow. Except for a period of intense activity while he held the Cavendish professorship at Cambridge, these papers appeared with remarkable regularity at the rate of about nine a year. Each records some definite clear-cut advance, and records it in a perfectly direct and unambiguous manner. Limitations of space prevent reference to more than the outstanding landmarks of his scientific life.

In the period between his first paper (1869) and his election to the Cavendish professorship (1879), Rayleigh's work dealt mainly with electrical questions, problems of light and colour, and dynamical questions of resonance and vibrations both of gases and of elastic solids. His investigations in these latter subjects ultimately formed the foundation of his Treatise on the Theory of Sound. This, the only textbook he ever wrote, was begun during his Egyptian tour in 1873, but was not published until 1877, when it at once took rank as the leading book on the subject, a position it has retained ever since.

In 1879 Clerk-Maxwell died, after holding for only eight years the Cavendish professorship of experimental physics which had been founded for him at Cambridge. In accordance with a widely-expressed wish, the professorship was re-established specially for Lord Rayleigh, and he was duly elected in December 1879. The taking up of his professorial duties not only marks the commencement of the most active period of his scientific life, but coincides also with a change in the nature of his papers. He thought it important that the energies of the laboratory under his charge should be devoted in the main to some one big problem of research in which all who wished could take part. The subject selected was a re-determination of the electrical units in absolute measure. Measurements had been made by a committee of the British Association in 1863, but doubt had been thrown on their accuracy, and a re-determination was urgently needed. The subject had the disadvantage of giving but little scope to the originality or intellectual powers of an ambitious student, but Rayleigh succeeded in persuading a band of workers, some of whom have since risen 515