196 



NATURE 



[July 2, 1903 



acoustical researches to the study of hydrodynamics. 

 Shortly after this his physiological work induced him 

 to again attack electrical problems. From the study 

 of electrical oscillations he proceeded to a discussion of 

 the most general form of expression for the potential 

 of single " Stromelemente," and of the differential 

 equations which determine the motion of electricity. 

 In this first treatise on electrodynamics, Helmholtz 

 aimed at giving a clear summary of all results pre- 

 viously obtained. 



In 1871 Helmholtz was appointed to the professor- 

 ship of physics at Berlin in succession to Magnus, 

 which post he held until 1888. From this time onward 

 he confined himself almost entirely to physics, and did 

 very little more physiological work. In the following 

 j'ear, after the marriage of his daughter Kathe, and a 

 visit to Scotland (where he met Tait, i\ndrews, Huxley, 

 Brown, Sylvester, &c., and found golf less easy to 

 master than science), he published further papers " On 

 the Theories of Electrodynamics." In these he re- 

 plied effectively to the criticisms of Bertrand, Weber, 

 &c., and, basing his researches on Neumann's potential 

 law, he investigated the various theories that had been 

 put forward, showing that Faraday's assumption of 

 dielectric polarity was the only theory consistent with 

 observed properties of open and closed circuits. For 

 a short time after this he applied his versatile genius 

 to the problem of artificial flight and guidable balloons, 

 made valuable contributions to the theory of the micro- ! 

 scope and anomalous dispersion, and turned his atten- ; 

 tion to the origin of thunderstorms. He then returned j 

 for some years to his researches in electricity, and 

 applied Faraday's theories to electrochemistry, pro- 

 ducing papers on electric currents in fluids and " elek- 

 trische Grenzschichten." . | 



In 1878 commenced his lifelong friendship with | 

 Hertz, whose investigations led Helmholtz back to his 

 ■electrodynamical researches, and to the discussion of i 

 the electromagnetic theory of light. In 1881 he again 

 visited England, where he delivered his famous 

 " Faraday lecture " (one of the best lectures he ever 

 gave), which was received with the greatest enthu- 

 siasm. The delivery of this discourse led him to 

 further investigations in electrochemistry, and in 

 ■*' The Thermodynamics of Chemical Processes," pub- 

 lished in 1883, he discusses the relations of chemical 

 combination, heat, and electrical potential, distinguish- 

 ing between the " free " energy of a system which can 

 he entirely converted into work and the " bound " 

 energy which cannot be so converted. After journeys 

 to Rome and England, he undertook a masterly de- 

 velopment of the principle of least action, a principle 

 which he considered as probably being the controlling 

 law of all reversible processes of nature. 



During the last year of his professorship at Berlin 

 Helmholtz returned to his work on electrical and 

 thermodynamical chemistry, and to the development 

 •of the " principle of the decrease of free energy in 

 chemical processes." In 1888 he was appointed presi- 

 dent of the newly-founded Physico-technical Institute, 

 a position in which he had comparative freedom from 

 routine work, and so was enabled still more thoroughly 

 .to devote himself to those investigations for which he 

 NO. 1757, VOL. 68] 



was so peculiarly fitted. His first great work in his 

 new position was the adaptation of the equations of 

 hydrodynamics to the case of layers of gases of vary- 

 ing density, and the application of his results to 

 meteorological phenomena. The remaining four years 

 of his life were devoted to more work on the mathe- 

 matical theory of electricity. The most importani 

 papers were those on the application of the principl( 

 of least action to Maxwell's electrodynamical equa- 

 tions, on the electromagnetic theory of colour dis- 

 persion, and on Maxwell's theory of the motion of the 

 ether. He died, after two months' illness, in 1894. 



Harold Hilton. 



THE EAKTH-HISTORY OF CENTRAL 

 EUROPE. 

 Central Europe. By Prof. Joseph Partsch, Ph.U. 

 Pp. xiv-t-358; with maps and diagrams. (London : 

 William Heinemann, 1903.) 



PROF. PARTSCH 'S geography of Central Europe 

 forms a volume of the series " Regions of the 

 World," edited by Mr. H. J. Mackinder. Written 

 in German, it has been well translated by Miss 

 Clementina Black, and has also undergone a little 

 condensation, probably to its advantage. On the 

 east and part of the south, the region has fairly de- 

 finite physical boundaries, in other directions they are 

 more often political; but practically Central Europe 

 includes the two great empires of Germany and 

 Austro-Hungary, with Switzerland, Belgium and the 

 Netherlands on the one hand, Montenegro, Servia, 

 Bulgaria and Roumania on the other. But in the 

 main there is a general correspondence between the 

 political and the physical boundaries of the region, 

 for Central Europe, geographically speaking, as Prof. 

 Partsch remarks, is a three-fold belt of Alps, of inferior 

 chains and of northern lowlands, and wherever one 

 of these elements dies out Central Europe comes to an 

 end. This is the best natural definition, though we 

 should have preferred the term central highlands to 

 " inferior chains," and a little clearer insistence on 

 the fact that the great mountain chains of Europe — 

 the Alps, Pyrenees and Carpathians— are compara- 

 tively modern physical upstarts, the highlands being 

 much more ancient regions, which, like some old 

 families, have come down in the world. Still, Prof. 

 Partsch makes it clear, in a chapter which certainly 

 would not stand any more compression, that the de- 

 velopment of Central Europe was a long and compli- 

 cated story. His remarks on traces in the Alps of valley 

 systems older than the present, illustrated by some 

 rough but sufficient diagrams after Prof. Heim, will 

 be very suggestive to students, though full justice can 

 hardly be done to the subject within the limits of this 

 volume, because mountain making in this region was 

 a complicated and intricate process, involving many 

 speculative elements. He does well also in calling 

 attention to the aggressive habit of some rivers; the 

 more active one cutting back through the old water 

 parting and capturing the other's tributaries. The 

 Maloya Pass affords, of course, a typical example of 



