Physics.—With astronomical science ranks, as a matter of course, physical science and the great discovery of the conservation or persistence of force, which now like an animating breath pervades all natural sciences, and deserves to be classed with the greatest discoveries of all time. Guessed and clearly predicted by Friedrich Mohr as early as 1837, this principle received its scientific confirmation from the German Robert Mayer (1842) and the Englishman Joule (1842-'49). Both these scientists had worked independently of each other. The validity of this great theory was first established by proving the identity of heat and motion (because proof as to these was easiest), and, the mechanical equivalent of heat having been calculated, was very soon fixed for all the forces of Nature. Thus the unity and immortality of force were demonstrated.
The physics of our century shows another great advance in what is called the kinetic theory of gases, for which Clausius and Maxwell paved the way, and which permits us a deep insight into the infinite fineness of matter and the inconceivable velocity of its internal motion. According to Clerk Maxwell, the most minute living being that can be seen under the most powerful microscope still contains a million (according to Tait, two million) organic molecules or atomic groups; so that we can not form any conception whatever of the incalculably great number of the finest histological elements for which perhaps no method of investigation is at our command. Finally, the century, shortly before its departure, has accomplished in the physical domain one of its most valuable feats by the discovery of the X or Röntgen rays, which permit our eye to penetrate to the innermost depths of objects hitherto regarded as opaque, and thereby make almost true the marvels of the Arabian Nights. Not less wonderful and unexpected is the success, likewise belonging to very recent time, attained by the experiments in liquefying and solidifying gases, like oxygen, nitrogen, carbonic acid, chlorine gas, and atmospheric air.
Chemistry.—As regards the domain of chemistry, this science, not to mention the numerous smaller discoveries important to industry and therapeutics, has achieved one of its greatest triumphs by its surprising penetration into the organic domain, and the consequent elucidation of the relation of the vegetable and animal metabolism. These discoveries, chiefly initiated by the renowned Liebig, in the years 1848-'55, were productive of the most beneficial results in the development of the physiological and medical sciences, as well as in agriculture. As a consequence of this knowledge, we have to greet the successful experiments in the artificial production of organic matter or the chemical synthesis inaugurated by the French chemist Berthelot in 1856. At present a whole series of genuine
