None of the processes of Nature, since the time when Nature began, have produced the slightest difference in the properties of any molecule. We are therefore unable to ascribe either the existence of the molecules or the identity of their properties to any of the causes which we call natural. On the other hand, the exact quality of each molecule to all others of the same kind gives it, as Sir John Herschel has well said, the essential character of a manufactured article, and precludes the idea of its being eternal and self existent."
The next year, 1874, a counterblast was delivered by Prof. Tyndall in his address at Belfast, as president of the Association. In it occurs the following passage: "Believing as I do, in the continuity of Nature, I cannot stop abruptly where our microscopes cease to be of use. Here the vision of the mind authoritatively supplements the vision of the eye. By an intellectual necessity I cross the boundary of the experimental evidence, and discern in that Matter which we, in our ignorance of its latent powers, and notwithstanding our professed reverence for its Creator, have hitherto covered with opprobrium, the promise and potency of all terrestrial life." Maxwell was present, and he sent to Blackwood's Magazine verses entitled "Notes of the president's address" in which the different points of the address are hit off very nicely.
After accepting the Cavendish professorship he unfortunately took on hand the work of editing the unpublished electrical researches, made 100 years before, by the Hon. Henry Cavendish, a member of the Devonshire family. The task cost him much time and labor which could have been better spent on his own unfinished projects, one of which was an Experimental Treatise on Electricity and Magnetism.
Mrs. Maxwell was now an invalid, and depended much on his care. In the spring of 1879 he himself began to be troubled with dyspeptic symptoms, especially with a painful choking sensation after eating meat; in the fall he sent for an Edinburgh physician to come to Glenlair, and was then informed that he had only a month to live. To get the best medical attention, he and his wife set out for Cambridge; the worst
