During the Middle Ages much of the scien tific knowledge of the ancients was irretrievably lost, and most of that which survived lay dor mant. The supreme authority of Aristotle among the scholastics, and their syllogistic methods of reasoning, prevented any advance ment of physical science by them. Only the alchemists, whose secret work must have dis covered (and lost) many a scientific truth; and a few inspired men among the scholastics, such as Roger Bacon, kept alive the spark of prog ress that burst into flame in the later Italian Renaissance with the work of Galileo Galilei. Galileo's experimental studies of the motion of falling bodies are the first of their kind, and may truly be said to date the beginning of mod ern science; although the studies in magnetism of his contemporary, William Gilbert, are scarcely less epochal. From then on the op position and persecution, which had so hindered progress on the part of Galileo and his prede cessors, weakened and finally broke down, and the development of the new science progressed rapidly. The history of the science can for a while now be outlined by mentioning great names. Torricelli, Pascal, von Guericke, and later Boyle, Mariotte and others discovered in quick succession the properties of the atmos phere and of gases and extended and unified the knowledge of hydrostatics. Huygens laid the foundations of physical optics, although building on them was deferred until nearly a century later. The list culminates in the name of Newton, who, born in the year that Galileo died, built upon the work of Galileo, and gave us our complete system of mechanics in his (Principia,) published in 1686-87. His experi mental investigations in light added greatly to the knowledge of that subject, although here he was unfortunate in his theoretical reasoning.
During a period which includes the 18th cen tury and the early part of the 19th century, the spread of popular interest in experimental sci ence, already noted in the foundation of the Royal Society of London in 1662, of the Academie des Sciences at Paris in 1666, and of the corresponding society at Berlin in 1700, stimulated scientific effort to an extent which made this period pre-eminently one of scien tific discovery. The names of Franklin, Caven dish, Black, Young, Fresnel, Galvam, Volta, Ohm, Ampere, Gauss, Davy and Faraday repre sent only a part of those whose brilliant dis coveries and clear thinking brought about such rapid advances in all branches of physics. Some of these, such as Franklin, Cavendish, Black and Davy, are to be recognized as men also promi nent in other and now far separated activities. This versatility is better understood when it is remembered that it was only after the discov eries of this period had added so much to the knowledge of natural philosophy, as all of physical science was then called, that its differ entiation into specialized sciences — physics, chemistry, etc.— began; and that, even after chemistry obtained individual recognition, physics formed the major portion of what re mained, and was known as natural philosophy for considerable time thereafter. The Indus trial Revolution in England about 1770, brought about as it was by scientific discoveries such as those which resulted in the invention of Watt's steam engine, had a profound reaction on scien tific discovery in the 19th century.
The discovery of electro-magnetic induction by Faraday in 1831 made possible the invention of the dynamo, whose commercial importance was at once recognized, and developments of commercial applications of electrical energy took place with great rapidity. In another direction a new tendency is to be noted in the establish ment, during the first half of the 19th century, under the leadership of Helmholtz, Mayer, Rumford and Joule of the principle of con servation of energy and of its universal appli cation. William Thomson (Lord Kelvin) was an important participator in this work, which he carried further by applying the principle to the co-ordination and extension of the theory of thermodynamics which had been so ably begun by Carnot and his contemporaries.
These two points of departure along new and divergent lines of development, between which experimental investigation continued to flourish, mark the beginning of the modern pe nod of science. The history of the commercial side is initiated by a remarkable series of bril liant inventions such as the telegraph, telephone, trans-Atlantic cable, incandescent lamp, electric traction, etc. i and its later details belong to electrical engineering. On the purely scientific side, development has been no less rapid, though until recently, less spectacular. Maxwell's genius early shaped the course of all later theo retical reasoning in electricity and light, while Kelvin developed much of the apparatus now used in electrical measurements. Joule, Ama gat, Andrews and others continued the experi mental studies begun by Charles and Regnault of the properties of gases, where later a spec tacular result was realized in the liquefaction of air and other gases.
The history of the later developments of this period has been touched upon in a previous section. Few discoveries stand out in their en tirety as do the discoveries of X-rays by Roent gen in 1896, of radio-activity by Becquerel the same year, or of radium by the Curies in 1898. The developments have been so varied, and much of the advancement has been by a process of growth through the combined efforts of so many men, that it must be left to the historian of 100 years hence to look back over this period and properly to adjudge its achievements.
No attempt is here made to even begin to give a complete bibliography of the science. This would be impossible. The following lists contain references to only a representative few of the more recent and more important publications in English, except that a fairly complete list of periodicals is given. Only general treatises are mentioned. For further study recourse should be had to the treatises covering the special topics of physics, and for these the reader is referred to the bibliographies under the corresponding arti cles included elsewhere in these volumes.
HisTosscaL—Cajori, F., 'A History of Physics' ; Barns, C., 'Progress of Physics in the Nineteenth Century> • Schuster, A., (Prog ress of Physics, 1875-1908> ; Williams, H. S. 'A History of Science,' and also (Nineteentli Century Science' ; Sedgwicic, W. T., and Tyler, H. W., 'A Short History of Science.>