Nevertheless he feels that although the evidence for the transmission of acquired habits is insufficient yet some connexion between variation and modification is suggested by the facts, understanding by "variations" departures of congenital origin and by "modifications" departures which are individually acquired. He has accordingly approached this subject from a new standpoint and has sketched in outline, Chapter 14, "an hypothesis according to which acquired modification may pave the way for congenital variation without any direct transmission as such." Prof. Lloyd Morgan does not accept Weismann's doctrine of germinal selection as recently expounded in The Monist though he regards it as a suggestive hypothesis; it does not follow for him that because in some cases use and disuse can have played no part therefore in no other cases has use-inheritance prevailed. He believes he can accept the facts adduced by the transmissionist and at the same time interpret them on selectionist principles. The gist of his idea is that "persistent modification through many generations, though not transmitted to the germ, nevertheless affords the opportunity for germinal variation of like nature." The modification is not inherited but from having taken place generation after generation variations in the same direction as the modifications are no longer repressed and are allowed full scope. There will arise a congenital predisposition to the modifications in question. Given the plasticity of organisms, given persistent modifications, ever increasing in adaptiveness, germinal variation will follow. The mod"ification as such is not inherited, but is the condition under which congenital "variations are favored and given time to get hold on the organism, and are thus "enabled by degrees to reach the fully adaptive level." The conclusions regarding heredity in man are important and touch the quick of a much vexed question. They approach again to the Weismannian view as will be seen from his own words: “There is little or no evidence of individually ac"'quired habits in man becoming instinctive through heredity. Natural selection "becomes more and more subordinate in the social evolution of civilised mankind; "and it would seem probable that with this waning of the influence of natural se"lection there has been a diminution also of human faculty. Hence there is little "'or no evidence of the hereditary transmission of increments of faculty due to con"tinued and persistent use. A discussion of heredity in man thus confirms the "'inference drawn from the study of habit and instinct in some of the lower ani"mals." And further: "If those who endeavor to apply biological conceptions to "social phenomena would only remember that the essence of natural selection is "the exclusion of the weakly, the inefficient, and the anywise unfit, from transmit"ting their inefficiency, and the consequent hereditary increment of efficiency in "those who remain to contribute as parents to the continuation of the race, much "confusion of thought would be avoided. In this sense I contend that natural "selection is not an important factor in human progress among the civilised races "of to-day." Prof. Lloyd Morgan does not believe that the level of human intelligence is rising but only the level of the intellectual and social environment—the stored up opportunities of intellectual and aesthetic culture. Selection without elimination involves no racial progress. He then puts this problem: "It would "seem, in fine, that if mental evolution in man be manifested rather in the pro"gressive advance of human achievement than in progressive increment of human "faculty; if the developmental process have been transferred from the individuals "to their environment; if it be rather the intellectual and moral edifice that is un"dergoing evolution, than the human builders that contribute in each generation a "few more stones to take a permanent place in its fabric; if there be thus no con"'clusive evidence that faculty is improving, but rather the opposite; if all this be "so, then it would seem that the ground is cut way from under the feet of those "who regard mental evolution in man as due to inherited increments of individ"ually acquired faculty. Nay, more; if the average level be not rising, some ex"planation must be demanded from transmissionists of this fact. For surely if "there be transmission of individually acquired increment, the average level of faculty ought to be steadily rising." The book, both for study and reading, is marked by charm of style, attractiveness of presentation, and soundness of philosophical view. There is a wealth of observation on animal life gathered in it, concisely and entertainingly told. All will draw intellectual edification from its perusal. T. J. MCC. VORLESUNGEN ÜBER THEORETISCHE PHYSIK. Von H. von Helmholtz. Band V Electromagnetische Theorie des Lichtes. Herausgegeben von Arthur König und Carl Runge. Hamburg. 1897. Pp. 370. Price, 14 Marks, Helmholtz in his triple rôle of physiologist, physicist, and mathematician is perhaps sometimes forgotten as Helmholtz the educator. It may indeed be doubted whether any one American, dead or living, has ever furnished from the ranks of his own students so many investigators and instructors in physics for American institutions as has Helmholtz. For a full quarter of a century, the royal university of Berlin was the attracting centre for Americans in search of opportunities in physics, mathematical or experimental. It was there, under the kindly eye and word of the master, that life-long inspiration came to many a student. The volume under review, therefore, is not without a peculiar personal interest for many of its English-speaking readers. Forming, as it does, the fifth in a series of six volumes, it is nevertheless the first to appear, the lectures having been recorded in stenographic notes by a student during the last semester of their delivery. While the Electromagnetic Theory of Light stands as the title of the lectures, they cover really the whole ground of modern optics, both geometrical and physical. Parts III., IV., and V., treating of spherical waves, diffraction and geometrical optics, respectively, would stand intact on any wave-theory of light, being questions of kinematics, not of kinetics. It is when the real nature of luminous disturbances is considered, in Parts I., II., and VI., that the electromagnetic theory is employed, and employed with marvellous lucidity. It will be remembered that Maxwell, in 1865, sent to the Royal Society his prediction that light-waves would be found to be electric waves, travelling in the ether of transparent substances, and that the speed of light, in any given medium, would be found to depend upon the electric and magnetic constants of that medium. But it was not until the autumn of 1888 that Hertz, the favorite pupil of Helmholtz, succeeded in actually producing these electric waves, in measuring their speed, in reflecting, refracting, and polarising them; succeeded, in short, in proving experimentally the identity of light-waves and electric-waves. This investigation of Hertz was undertaken in response to a prize question set by Helmholtz for the Berlin Academy. In a very true sense, therefore, Helmholtz is one of the founders of the electromagnetic theory of light: and the volume before us is one in which a creator describes his own work; especially is this the case in the chapters on geometrical optics and dispersion. To one of philosophic bent, no more instructive chapter in the history of physical science is to be found than that in which a great field of learning-light-is swallowed up, as a special case, in another great field-electricity. It forms a long stride toward a unitary view of nature, toward the goal of modern physics. Each of the various parts of the subject which Helmholtz here handles have been discussed in various treatises, English and German, and, indeed, the whole subject is touched upon in certain compendiums of physics. But nowhere has there ever appeared a treatment at once so thorough, so elegant, and so exceedingly clear, as that under review. The mathematics which appear are not introduced as exercises in analysis, rather as tools in a master's hand. Each mathematical result receives a distinct physical interpretation. The word "theory," from its first appearance on the title-page to the end of the book, is employed only in its best sense -its original sense-to indicate not the hazy guess of a vivid imagination, but an attempt at a comprehensive survey and a concise description of facts. A brief summary of the contents of the volume is the following. Our notions concerning the nature of light have been arrived at through at least four steps. First, the emission-theory of Empedocles in which the eye, as well as the object seen, emits the light. Second, the corpuscular theory of Newton, in which the self-luminous body is the sole source of emission. Third, the elastic-solid wavetheory of Fresnel. Fourth, the electromagnetic wave-theory of Maxwell. It is to a complete description of optical phenomena in terms of Maxwell's idea that this first purely didactic volume of Helmholtz is devoted. One hundred pages are first given to a study of the properties of electric waves. The beautiful parallel treatment of electric and magnetic quantities is preserved throughout. A clear grasp of the general phenomena of electricity is here demanded of the intelligent reader. The next hundred pages cover a rigid mathematical discussion of diffraction. It is here that the author explains what is, at once, the par adox and the crux of optical science, viz., the rectilinear propagation of light, and the fact that light can and does shine around a corner. The starting-point of this discussion is a remarkable generalisation of Green's Theorem-itself the most powerful theorem in mathematical physics-to include four independent variables, time being the one added to the usual three space-coordinates. Geometrical optics is the subject of the third hundred pages, a very elegant chapter. The remainder of the book goes to dispersion and polarisation, treated in terms of the electromagnetic theory. Much of the subject matter is the result of Helmholtz's own investigations concerning the mysterious connexion between ether and matter. The appearance of these six posthumous volumes of mathematical physics, in addition to three volumes of Scientific Papers and two epoch-making treatises, cannot be contemplated without amazement at the changes which the genius of this one man has wrought on the face of modern science. The ease with which he lays aside his seven-leagued boots and adapts himself to the intellectual wants of his hearers makes him a brilliant example to all teachWhile as an instructor in the elementary parts of his subject he was never a striking success, to investigators the mere mention of his name is an inspiration. ers. OSTWALD'S Klassiker der exakten WISSENSCHAFTEN. HENRY CREW. Vier Abhandlungen über die Elektricität und den Magnetismus (No. 13.) The four essays of Coulomb here reprinted are the most important of his seven fundamental memoirs on the laws of electricity and magnetism. The first two are devoted to the proof that the repulsions and attractions of electrified and magnetised bodies take place according to the law of the inverse squares, the third deals with the loss of electricity in such action, the fourth proves that the electric charge is distributed over bodies by its own repulsion, and that when in equilibrium it is always at the surface. The results form the basis of the entire mathematical treatment of magnetic and electrostatic phenomena as it has taken shape in the modern theory of potential, and until the researches of Faraday formed the sole basis. Revolution after revolution has taken place since then in electrical theory, but the facts established by Coulomb remain unchanged, and his investigations, therefore may be regarded as an exemplar of scientific procedure. The memoirs of Lavoisier and Laplace are extremely important as marking the starting-point of the investigations which led up to the thermal theories of J.R. Mayer, Krönig, Clausius, and others, and in view of the frequent references to them in books on the history of the conservation of energy, it is well that they can be obtained in a separate and cheap form. Lambert's researches are the first general investigations on cartography and form collaterally valuable contributions to pure mathematics. The thread of investigation in this field was continued by Lagrange, who, while still generalising the methods of treatment, aimed, as was always his wont, at obtaining practically useful results. With Gauss, emphasis was principally laid upon the abstract mathematical point of view. The publication of this series is a valuable work, and all students should possess the Classics which relate to their departments. μ. ELEMENTS OF THEORETICAL PHYSICS. By Dr. C. Christiansen, Professor of Physics in the University of Copenhagen. Translated into English by W. F. Magie, Ph. D., Professor of Physics in Princeton University. London and New York: The Macmillan Co. 1897. Pages, 339. Price, $3.25. Of the flood of recent text-books on physics the treatise of Professor Christiansen has stood high in pedagogical favor. It exists at least in a German translation and has now been Englished by Prof. W. F. Magie of Princeton University. The book is not an elementary one, and requires considerable knowledge of mathematics, but it is condensed and treats the main problems of theoretical physics in a concise and direct manner. There are fourteen chapters in all, entitled as follows: "General Theory of Motion," "The Theory of Elasticity," "Equilibrium of Fluids," Motion of Fluids," 'Internal Friction," "Capillarity," "Electrostatics," "Magnetism," "Electro-Magnetism," "Induction," Electrical Oscillations," "Refraction of Light in Isotropic and Transparent Bodies," Thermodynamics," and "Conduction of Heat." American text-books of physics, having a different purpose in view, devote the greater part of their space to the discussion of methods and instruments, so that a treatise like Christiansen's which is almost totally abstract and mathematical will find the field virtually unoccupied. The translation is good, and the publishers are to be congratulated upon the excellent mechanical makeup of the book. 44 μικρκ. UEBER DEN Urstoff und seine Energie. I. Theil. Eine physikalish-chemische Untersuchung über die theoretische Bedeutung der Gesetze von DulongPetit und Kopp auf der Grundlage einer kinetischen Theorie des festen Aggregatzustandes. Von Dr. Phil. H. Keller. Leipsic: B. G. Teubner. 1896. Pages, 58. Price, M. 2. The problem of the prima materia has occupied philosophical brains for more than two thousand years, and after having been laid to rest by modern philosophical criticism as the vision of a metaphysical dream, has now again come to the fore |