“The form and dimensions of the orbits of the planets, for instance, are not determined by any law of nature, but depend upon a particular collocation of matter. The same is the case with respect to the size of the earth, from which the standard of what is called the metrical system has been derived. But these astronomical and terrestrial magnitudes are far inferior in scientific importance to that most fundamental of all standards which forms the base of the molecular system. Natural causes, as we know, are at work which tend to modify, if they do not at length destroy, all the arrangements and dimensions of the earth and the whole solar system. But though in the course of ages catastrophes have occurred and may yet occur in the heavens, though ancient systems may be dissolved and new systems evolved out of their ruins, the molecules out of which these systems are built--the foundation stones of the material universe--remain unbroken and unworn. They continue this day as they were created--perfect in number and measure and weight; and from the ineffaceable characters impressed on them we may learn that those aspirations after accuracy in measurement, and justice in action, which we reckon among our noblest attributes as men, are ours because they are essential constituents of the image of Him who in the beginning created, not only the heaven and the earth, but the materials of which heaven and earth consist.” This was criticised in _Nature_ by Mr. C. J. Munro, and at a later time by Clifford in one of his essays. Some correspondence with the Bishop of Gloucester and Bristol on the authority for the comparison of molecules to manufactured articles is given by Professor Campbell, and in it Maxwell points out that the latter part of the article “Atom” in the _Encyclopædia_ is intended to meet Mr. Munro’s criticism. In 1874 the British Association met at Belfast, under the presidency of Tyndall. Maxwell was present, and published afterwards in _Blackwood’s Magazine_ an amusing paraphrase of the president’s address. This, with some other verses written at about the same time, may be quoted here. Professor Campbell has collected a number of verses written by Maxwell at various times, which illustrate in an admirable manner both the grave and the gay side of his character. BRITISH ASSOCIATION, 1874. _Notes of the President’s Address._