HEINRICH

RUDOLF

See also:

• HEINRICH RUDOLF HERTZ (1857-1894)
• HERTZ, HENRIK (1797–1870)

HERTZ (1857-1894)  , German physicist, was born at Hamburg on the 22nd of February 1857 . On leaving school he determined to adopt the profession of engineering, and in the pursuance of this decision went to study in Munich in 1877 . But soon coming to the conclusion that engineering was not his vocation he abandoned it in favour of physical science, and in October 1878 began to attend the lectures of G . R . Kirchhoff and H. von Helmholtz at Berlin . In preparation for these he spent the winter of 1877–1878 in reading up original treatises like those of Laplace and Lagrange on mathematics and mechanics, and in attending courses on practical physics under P . G. von Jolly and J . F . W. von Bezold; the consequence was that within a few days of his arrival in Berlin in October 1878 he was able to plunge into original research on a problem of electric inertia . For the best solution a prize was offered by the philosophical faculty of the University, and this he succeeded in winning with the paper which was published in 188o on the " Kinetic Energy of Electricity in Motion." His next investigation, on " Induction in Rotating Spheres," he offered in 188o as his dissertation for his doctor's degree, which he obtained with the rare distinction of summa cum laude . Later in the same year he became assistant to Helmholtz in the physical laboratory of the Berlin Institute . During the three years he held this position he carried out researches on the contact of elastic solids, hardness, evaporation and the electric discharge in gases, the last earning him the special commendation of Helmholtz .

In 1883 he went to

Kiel, becoming PrivatdozQnt, and there he began the studies in Maxwell's electro-magnetic theory which a few years later resulted in the discoveries that rendered his name famous . These were actually made between 1885 and 1889, when he was professor of physics in the Carlsruhe Polytechnic . He himself recorded that their origin is to be sought in a prize problem proposed by the Berlin Academy of Sciences in 1879, having reference to the experimental establishment of some relation between electromagnetic forces and the dielectric polarization of insulators . Imagining that this would interest Hertz and be successfully attacked by him, Helmholtz specially drew his attention to it, and promised him the assistance of the Institute if he decided to work on the subject; but Hertz did not take it up seriously at that time, because he could not think of any procedure likely to prove effective . It was of course well known, as a necessity of Maxwell's mathematical theory, that the polarization and depolarization of an insulator must give rise to the same electromagnetic effects in the neighbourhood as a voltaic current in a conductor . The ex perimental proof, however, was still lacking, and though several experimenters had come very near its discovery, Hertz was the first who actually succeeded in supplying it, in 1887 . Continuing his inquiries for the next year or two, he was able to discover the progressive propagation of electromagnetic action through space, to measure the length and velocity of electromagnetic waves, and to show that in the transverse nature of their vibration and their susceptibility to reflection, refraction and polarization they are in complete correspondence with the waves of light and heat . The result, was in Helmholtz's words, to establish beyond doubt that ordinary light consists of electrical vibrations in an all-pervading ether which possesses the properties of an insulator and of a magnetic medium . Hertz himself gave an admirable account of the significance of his discoveries in a lecture on the relations between light and electricity, delivered before the German Society for the Advancement of Natural Science and Medicine at Heidelberg in September 1889 . Since the time of these early experiments, various other modes of detecting the existence of electric waves have been found out in addition to the spark-gap which he first employed, and the results of his observations, the earliest interest of which was simply that they afforded a confirmation of an abstruse mathematical theory, have been applied to the practical purposes of signalling over considerable distances (see TELEGRAPHY, WIRELESS) . In 1889 Hertz was appointed to succeed R . J .

E .

Clausius as ordinary professor of physics in the university of Bonn . There he continued his researches on the discharge of electricity in rarefied gases,. only just missing the discovery of the X-rays described by W . C . Rontgen a few years later, and produced his treatise on the Principles of Mechanics . This was his last work, for after a long illness he died at Bonn on the 1st of January 1894 . By his premature death science lost one of her most promising disciples . Helmholtz thought him the one of all his pupils who had penetrated farthest into his own circle of scientific thought, and looked to him with the greatest confidence for the further extension and development of his work . Hertz's scientific papers were translated into English by Professor D . E . Jones, and published in three volumes: Electric Waves (1893), . Miscellaneous Papers (1896), and Principles of Mechanics (1899) .

The

preface contributed to the first of these by Lord Kelvin, and the introductions to the second and third by Professors P . E . A . Lenard and Helmholtz, contain many biographical details, together with statements of the scope and significance of his investigations .