Niven, in his preface to the collected papers dealing with this book, writes thus:—
“This work, published in 1879, has had the effect of increasing the reputation of Cavendish, disclosing as it does the unsuspected advances which that acute physicist had made in the Theory of Electricity, especially in the measurement of electrical quantities. The work is enriched by a variety of valuable notes, in which Cavendish’s views and results are examined by the light of modern theory and methods. Especially valuable are the methods applied to the determination of the electrical capacities of conductors and condensers, a subject in which Cavendish himself showed considerable skill both of a mathematical and experimental character.
“The importance of the task undertaken by Maxwell in connection with Cavendish’s papers will be understood from the following extract from his introduction to them:—
“‘It is somewhat difficult to account for the fact that though Cavendish had prepared a complete description of his experiments on the charges of bodies, and had even taken the trouble to write out a fair copy, and though all this seems to have been done before 1774, and he continued to make experiments in electricity till 1781, and lived on till 1810, he kept his manuscript by him and never published it.
“‘Cavendish cared more for investigation than for publication. He would undertake the most laborious researches in order to clear up a difficulty which no one but himself could appreciate or was even aware of, and we cannot doubt that the result of his enquiries, when successful, gave him a certain degree of satisfaction. But it did not excite in him that desire to communicate the discovery to others, which in the case of ordinary men of science generally ensures the publication of their results. How completely these researches of Cavendish remained unknown to other men of science is shown by the external history of electricity.’
“It will probably be thought a matter of some difficulty to place oneself in the position of a physicist of a century ago, and to ascertain the exact bearing of his experiments. But Maxwell entered upon this undertaking with the utmost enthusiasm, and succeeded in identifying himself with Cavendish’s methods. He showed that Cavendish had really anticipated several of the discoveries in electrical science which have been made since his time. Cavendish was the first to form the conception of and to measure Electrostatic Capacity and Specific Inductive Capacity; he also anticipated Ohm’s law.”
During the last years of his life Mrs. Maxwell had a serious and prolonged illness, and Maxwell’s work was much increased by his duties as sick nurse. On one occasion he did not sleep in a bed for three weeks, but conducted his lectures and experiments at the laboratory as usual.
About this time some of those who had been “Apostles” in 1853–57 revived the habit of meeting together for discussion. The club, which included Professors Lightfoot, Hort and Westcott, was christened the “Eranus,” and three of Maxwell’s contributions to it have been preserved and are printed by Professor Campbell.
After the Cavendish papers were finished, Maxwell had more time for his own original researches, and two important papers were published in 1879. The one on “Stresses in Rarefied Gases arising from Inequalities of Temperature” was printed in the Royal Society’s Transactions, and deals with the Theory of the Radiometer; the other on “Boltzmann’s Theorem” appears in the Transactions of the Cambridge Philosophical Society. In the previous year he had delivered the Rede lecture on “The Telephone.” He also began to prepare a second edition of “Electricity and Magnetism.”
His health gave way during the Easter term of 1879; indeed for two years previously he had been troubled with dyspeptic symptoms, but had consulted no one on the subject. He left Cambridge as usual in June, hoping that he would quickly recover at Glenlair, but he grew worse instead. In October he was told by Dr. Sanders of Edinburgh that he had not a month to live. He returned to Cambridge in order to be under the care of Dr. Paget, who was able in some measure to relieve his most severe suffering but the disease, of which his mother had died at the same age, continued its progress, and he died on November 5th. His one care during his last illness was for those whom he left behind. Mrs. Maxwell was an invalid dependent on him for everything, and the thought of her helplessness was the one thing which in these last days troubled him.