as imagined by Hobbes, is unquestionable; but how Mr. Mill could describe that union as chemical, and as analogous to the compound formed like water, by hydrogen and oxygen, is inexplicable if it be remembered that the composition of water was not discovered by Cavendish till 1784—thirty-five years after the appearance of the "Observations"—and that Chemistry only passed from the metaphysical to the positive stage with the deposition of phlogiston by Priestley and Lavoisier in the last quarter of the century. The following quotations from Hartley himself will confirm this a priori argument by showing the real nature of association as figured by him:
"Upon the whole, it may appear to the Reader, that the simple Ideas of Sensation must ruu into Clusters and Combinations, by Association; and that each of these will, at last, coalesce into one Complex Idea, by the Approach and Commixture of the several compounding Parts."[1]
No chemist would describe chemical union as "coalescence," or speak of the new substance produced by the operation of affinity as made up of "clusters and combinations" by the "approach and commixture" of parts. As appears still more clearly when Hartley proceeds to explain and illustrate this "coalescence," he had in his mind, as the physical type of his conception, no more "intimate union" than that combination of different kinds of matter called solution:[2]
"If the Number of simple Ideas which compose the complex one be very great, it may happen that the complex Idea shall not appear to bear any relation to these its compounding Parts, nor to the external Senses upon which the original Sensations, which gave Birth to the compounding Ideas, were impressed. The Reason of this is, that each single Idea is overpowered by the Sum of all the rest, as soon as they are all intimately united together. Thus, in very compound Medicines, the several Tastes and Flavors of the separate Ingredients are lost and overpowered by the complex one of the whole Mass: so that this has a Taste and Flavor of its own, which appears to be simple and original, and like that of a natural Body."[3]
We should be disposed to describe Hartley's view of mental composition as bearing a similar relation to James Mill's synthesis as Newton's composition of light to Goethe's theory of colors—as implying some species of union closer than the mechanical and less binding than the chemical. Thomas Brown clearly stated the law-as chemically conceived, in one of his introductory lectures. In mere statement James Mill's exposition is no advance upon Brown's, but the law took enormous extensions in his hands, and was applied to the senses, the feelings, memory, classification, language, ratiocination, the will, belief, etc. Something has been added to his synthesis, and a little has been taken from it, but he appears to have made as much as could be made out of the bare laws of association, unextended to the rest of
