tant discovery that the luminiferous undulations are lateral not longitudinal, he says that it showed "a sagacity which would have done honor to Newton himself." Just naming the discovery of latent heat by Black, the discrimination by Wollaston of quantity and intensity in electricity, and the disclosure of electrolysis by Nicholson and Carlisle (all of them cardinal discoveries) and passing over minor contributions to physical science, we come to the great contributions of Faraday—magneto-electricity, the quantitative law of electrolysis, the magnetization of light, and diamagnetism: not mentioning others of much significance. Next there is the great truth which men still living have finally established—the correlation and equivalence of the physical forces. In the establishment of this truth Englishmen have had a large share—some think the larger share. Remembering that in England the conception of heat as a mode of motion dates from Bacon, by whom it is expressed with an insight that is marvellous considering the knowledge of his time—remembering, too, that "Locke stated a similar view with singular felicity;" we come, among Englishmen of the present century, first to Davy, whose experiments and arguments so conclusively supported those of Rumford; then to the view of Roget and the postulate on which Faraday habitually reasoned, that all force arises only as other force is expended; then to the essay of Grove, in which the origin of the various forms of force out of one another was abundantly exemplified; and finally to the investigations by which Joule established the quantitative relations between heat and motion. Without dwelling on the important deductions from this great truth made by Sir W. Thomson, Rankine, Tyndall, and others, I will merely draw attention to its highly-abstract nature as again showing the baselessness of the above-quoted notion.
Equally conclusive is the evidence when we pass to Chemistry. The cardinal value of the step made by Dalton, in 1808, when the aperçu of Higgins was reduced by him to a scientific form, will be seen on glancing into Wurtz's "Introduction to Chemical Philosophy," and observing how the atomic theory underlies all subsequent chemical discovery. Nor, in more recent days, has the development of this theory fallen unduly into foreign hands. Prof. Williamson, by reconciling the theory of radicals with the theory of types, and by introducing the hypothesis of condensed molecular types, has taken a leading part in founding the modern views of chemical combinations. We come next to the cardinal conception of atomicity. In 1851, Prof. Frankland initiated the classification of the elements by their atomicities: his important generalization being now avowedly accepted in Germany by those who originally disputed it; as by Kolbe in his "Moden der Modernen Chemie." On turning from the more general chemical truths to the more special chemical truths, a like history meets us. Davy's discovery of the metallic bases of the alkalies and earths was an all-important step. Passing over many other achieve-
