The wonderfully beautiful experiments of Sir William Crookes, on the passage of an electric discharge through a high vacuum, and other phenomena connected with what has been called “radiant matter,” begun about a quarter of a century ago and continued by him and others up to the present time, laid the foundation for the brilliant work of Röntgen in the discovery and study of the so-called “X”-rays, the real nature of which is not yet understood. Their further investigation by J. J. Thomson, Becquerel, and others, seems to have revealed new forms and phases of radiation, a fuller knowledge of which is likely to throw much light on obscure problems relating to the nature of matter. Concerning the “Nature of Matter,” the ablest physicists of the century have thought and written much, and doubtless our present knowledge of the subject is much more nearly the truth than that of a hundred years ago. The molecular theory of gases has met with such complete experimental verification, and is so in accord with all observed phenomena, that it must be accepted as essentially correct. As to the ultimate nature of what is called matter, as distinguished from the ethereal medium, what is known as the “vortex theory of atoms” has received the most consideration. This theory was developed by Lord Kelvin out of Helmholtz’s mathematical demonstration of the indestructibility of a vortex ring when once formed in a medium possessing the properties which are generally attributed to the ether. Perhaps the most remarkable as well as the most promising fact relating to physical science at the close of the nineteenth century is the great and rapidly increasing number of well-organized and splendidly equipped laboratories in which original research is systematically planned and carried out. When one reflects that for the most part during the century just ended the advance of science was more or less of the nature of a guerrilla warfare against ignorance, it seems safe to predict for that just beginning victories more glorious than any yet won. T. C. MENDENHALL. WAR It is doubtful how far, even if as civilians we get over our natural dislike of talking of military change as “progress,” there has been any considerable advance in the larger aspects of military science within the century. The genius of Bonaparte, working upon the foundations laid by Frederick the Great, established a century ago principles which are essentially applicable to the military matters of the present day; and although the scientific developments of artillery and musketry have affected the dispositions of battle-fields, the essential principles of the art of preparation for war and of strategy stand where they stood before.