488 POPULAR SCIENCE MONTHLY. 



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 per- 

 vades all natural sciences, and deserves to be classed with the greatest 

 discoveries of all time. Guessed and clearly predicted by Fried- 

 rich Mohr as early as 1837, this principle received its scientific con- 

 firmation from the German Eobert Mayer (1842) and the English- 

 man Joule (1842-49). Both these scientists had worked inde- 

 pendently 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 Na- 

 ture. 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 Max- 

 well paved the way, and which permits us a deep insight into the 

 infinite fineness of matter and the inconceivable velocity of its in- 

 ternal motion. According to Clerk Maxwell, the most minute liv- 

 ing 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 dis- 

 covery of the X or Rontgen rays, which permit our eye to pene- 

 trate to the innermost depths of objects hitherto regarded as opaque, 

 and thereby make almost true the marvels of the Arabian Mghts. 

 Not less wonderful and unexpected is the success, likewise belong- 

 ing 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 in- 

 dustry and therapeutics, has achieved one of its greatest triumphs 

 by its surprising penetration into the organic domain, and the conse- 

 quent elucidation of the relation of the vegetable and animal me- 

 tabolism. 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 or- 

 ganic matter or the chemical synthesis inaugurated by the French 

 chemist Berthelot in 1856. At present a whole series of genuine 



