1922 Encyclopædia Britannica/Bjerknes, Vilhelm

From Wikisource
Jump to: navigation, search

BJERKNES, VILHELM (1862- ), Norwegian physicist, son of Carl Anton Bjerknes, professor of mathematics in the university of Christiania, was born in 1862, and was educated at the university of Christiania. He became at a very early age assistant to, and collaborator with, his father, who had discovered by mathematical analysis the remarkable apparent actions at a distance between pulsating and oscillating bodies in a fluid, and their analogy with the electric and magnetic actions at a distance. Apparently no attempt had been made to demonstrate experimentally the theories arrived at by the older professor until his son, then a lad of about 17 or 18 years of age, turned his mathematical knowledge and remarkable mechanical genius to the devising of a series of instruments, by which all the well-known phenomena of electricity and magnetism were illustrated and reproduced, by spheres and discs and membranes, set into rhythmic vibration in a bath containing a viscous fluid such as syrup. These remarkable demonstrations formed the most important exhibit in the department of physics at the Exposition Internationale d'Électricité held in Paris in 1881, and aroused the greatest interest in the scientific world.

The younger Bjerknes studied electric waves (1890-1) in Bonn, Germany, in the laboratory of Hertz, where he succeeded in giving the explanation of the phenomenon called “multiple resonance,” discovered by Sarasin and De la Rive. Continuing his experiments at the university of Christiania (1891-2), he proved experimentally the influence which the conductivity and the magnetic properties of the metallic conductors exert upon the electric oscillations, and measured the depth to which the electric oscillations penetrate in metals of different conductivity and magnetic permeability (the “skin effect”). Finally he furnished (1895) a complete theory of the phenomenon of electric resonance, involving a method of utilizing resonance experiments for the determination of the wave lengths, and especially of the damping (the logarithmic decrement) of the oscillations in the transmitter and the receiver of the electric oscillations. These methods from that time have been in continuous use, and have contributed much to the development of wireless telegraphy. His papers on electric oscillations were published in Annalen der Physik (1891-5). In 1895, after he had been appointed to the newly created professorship of mechanics and mathematical physics at the university of Stockholm, where he had been lecturer since 1893, he returned to hydrodynamic investigations, pursuing them in two different directions. In his Vorlesungen über Hydrodynamische Fernkräfte nach C. A. Bjerknes Theorie (1900-2) he gave the first complete mathematical and experimental exposition of the discoveries of his father, whose age and excessive self-criticism had prevented him from finishing his work himself; and in a later book, Die Kraftfelder (1909), he stated the same theory in a very much generalized form according to methods of his own. On the other hand, he developed in 1898 the general law for the formation of circulations and vortices in a frictionless fluid, and began to apply the general vortex theory to atmospheric and oceanic motions. This attack upon the meteorological problems from a hydrodynamical point of view was after 1906 supported by the Carnegie Institution of Washington, of which he became a Research Associate. Two introductory volumes, Statics and Kinematics, of a greater work, Dynamic Meteorology and Hydrography, were published in 1913 under the auspices of the Institution.

In 1907 he was called back to the university of Christiania, where a personal professorship of mechanics and mathematical physics was created for him. In 1912 he was called to the university of Leipzig to create there a new professorship of geophysics and to organize, according to his own plans, a Geophysical Institute for atmospheric investigations. There, in 1916, he started the publication Synoptische Darstellung atmosphärischer Zustände über Europa; but in 1917 he returned to Norway, where he was attached, as professor of geophysics, to the new Geophysic Institute in the city of Bergen. He was the originator there of an improved and more scientific weather service, afterwards controlled by his son and collaborator, Jakob Bjerknes (b. 1897), which occasioned a new view of cyclones and anticyclones as waves in a surface of discontinuity separating air of polar from air of more equatorial origin, and cutting the ground along a line which can be followed on the weather maps, now generally called “the polar front.” In 1893 Bjerknes married Honoria Bonnevie, who in earlier years assisted him much in his scientific work.