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nineteenth century is distinguished for the advance of science and the spread of democracy, and science is dominant as its applications have supplied the economic conditions that make democracy possible—general education, relative leisure and comparatively broad interests for a majority of the people. We may consequently regard it as probable that the greatest men of the century were its scientific leaders, and that they will ultimately be held in higher honor than the authors or artists, than the statesmen or soldiers. The doctrines of the conservation of energy and of organic evolution are the two greatest generalizations of modern science. Each has had its historical development both before and after, but is primarily associated with the one great name. We may believe that in the future everything connected with the life and work of Helmholtz or of Darwin will be of the deepest interest, and it is fortunate that the biographies that have been published are so adequate. "The Life and Letters of Charles Darwin," by his son. Dr. Francis Darwin, with the supplementary volumes of letters give a sympathetic and vital reflection of the noble and simple man and of his performance. The biography of Hermann von Helmholtz by Professor Leo Königsberger makes a more mechanical impression, but it gives a correct and useful account of the vast range of work accomplished by Helmholtz, and those facts of his private life that can be related objectively.

This biography published in 1902 and 190.3 has been abridged and translated into English by Lady Welby, with a preface by Lord Kelvin, and is now published by the Clarendon Press of Oxford. Of the eight portrait plates in the original, three are reproduced in the translation. In the two portraits by Lenbach the features are somewhat idealized. The bust by Hildebrand, made in 1891, is not given in the English volume, but more truly represents Helmholtz as he appeared during his visit to America toward the end of his life.

The paper on the conservation of energy, printed separately in 1847, after having been rejected by the leading German physical journal, may have been technically anticipated by Mayer and Joule, but it is the cornerstone of modern physical science. When this paper was published, Helmholtz was an army surgeon at Potsdam, his father, who was a teacher of classical languages, not being able to afford the cost of a university education. Thanks to von Humboldt, he was released from the army to become teacher of anatomy in the Berlin Academy of Arts. During his whole life, Helmholtz was deeply interested in the plastic arts, in music and in literature, thus demonstrating that there is no incompatibility between science and the fine arts. Of equal significance is his constant concern with philosophy.

Helmholtz became professor of physiology at Königsberg in 1849; he removed to Bonn in 1855 and to Heidelberg in 1858, remaining there for thirteen years. During this period he measured the velocity of the nervous impulse and prepared his great works on vision and on hearing, of which the ophthalmoscope was a by-product. Helmholtz's primary interests were always in mathematical physics, and he