NA TURE 



121 



THURSDAY, JUNE 7, 1883 



WIEDEMANN'S " ELECTRICITY " 

 Die Lehre von der Ekctricitdt. Von Gustav Wiedemann. 

 Vol. I.j pp. xi. and 795 (1882) ; Vol. II., pp. vii. and 

 1002(1883). (Braunschweig: Vieweg.) 



FOR more than twenty years Prof. Wiedemann's 

 " Lehre vom Galvanismus und Elektromagnetismus," 

 first published in iS6r, has been recognised without ques- 

 tion as the leading authority and great storehouse of facts 

 on the branch of science of which it treats. It is a prac- 

 tically exhaustive treatise, and each of the two editions 

 (second edition, 1S72 to 1874) marks with wonderful 

 accuracy the high- water mark of knowledge of its subject 

 up to the date of publication. It is safe to assume that 

 any fact that is not to be found recorded in its pages had 

 not been discovered, or at least had not been published, 

 up to the date of completion of whichever edition is 

 examined. The fulness and accuracy of the references 

 to original authorities give to Prof. Wiedemann's book a 

 unique value also as a classified index to the literature of 

 galvanic electricity and electromagnetism. 



The work which forms the subject of this notice, is in 

 one sense a third edition of the "Lehre vom Galvanismus." 

 It appears however under a new title, and is in fact to a 

 great extent a new book. It is characteristic of the 

 direction taken by the advance of electrical science 

 during the last twenty years that, while Prof. Wiedemann 

 found it practicable to confine himself in his first and 

 second editions almost exclusively to the phenomena of 

 current electricity and of magnetism, he has found it 

 advisable in the present edition to enlarge the scope of 

 his work so as to make it include the whole range of elec- 

 trical science. It is true that the second edition contains 

 an important chapter devoted to the discussion of a 

 phenomenon that has usually been considered in connec- 

 tion with statical electricity, namely, the disruptive dis- 

 charge in gases of different densities ; but this is almost 

 the only part of the book in which the considerations that 

 have to be dealt with in treating of electrostatics occupy 

 a prominent place. It is however becoming less and less 

 possible to treat satisfactorily of one branch of electricity 

 apart from the remainder. The terms friction al elec- 

 tricity and galvanic electricity have evidently an historical 

 rather than a scientific origin. They do not refer to any 

 logical classification of phenomena, but to two among the 

 many processes by which electrical effects can be origin- 

 ated. It is not even by any means certain that electri- 

 fication by friction is fundamentally a distinct phenomenon 

 from electrification by contact as this occurs in a gal- 

 vanic cell ; on the contrary, various recent investigations 

 tend to show that these actions are essentially similar, 

 and that the friction which takes place in one case is of 

 the nature of an accidental accompaniment. As a matter 

 of fact, however, an electrical machine acting by friction 

 serves (or at least did so until recently) as the readiest 

 means of producing one large class of electrical pheno- 

 mena ; while a galvanic or voltaic battery serves (or at 

 least did so until recently) as the readiest means of pro- 

 ducing another large class of phenomena. Thus the 

 division of electrical science for the purposes of study 

 Vol. xxviii. — No. 710 



into frictional electricity and galvanic electricity originated 

 in considerations of experimental convenience rather than 

 in any strictly scientific distinction. So far as such a 

 distinction can be drawn between these two branches, it 

 may be said that the former includes the study of all 

 those phenomena in which difference of potentials is the 

 most characteristic factor ; while the latter includes the 

 study of phenomena characterised by the transfer of 

 electricity. As examined by the instruments in use five- 

 and-twenty years ago, the effects produced by the elec- 

 trical machine seemed distinct enough from those due to 

 the galvanic battery — indeed the difficulty rather was to 

 establish their mutual connections ; but with the galvano- 

 meters and electrometers that are now — thanks to Sir 

 William Thomson — in the hands of every electrician, 

 nothing is easier than to measure the current of an elec- 

 trical machine or the difference of potentials of a galvanic 

 cell. Moreover the recent rapid development of methods 

 of converting mechanical into electrical energy, through 

 the agency of magneto-electric induction, has made us 

 familiar with the production of currents of great strength 

 associated with great differences of potential. It is, how- 

 ever, not only the introduction of new instruments and 

 apparatus, and the increased power over electrical pheno- 

 mena that modern experimentalists have thereby acquired, 

 that make it less possible now than formerly to treat of 

 the laws of electric currents without reference to the prin- 

 ciples of electrostatics. The conception that the imme- 

 diate cause of the phenomena exhibited in either an 

 electric or a magnetic field has its seat, not in electrified 

 conductors, or in magnets or conducting wires, but in an 

 impalpable medium existing throughout space, has com- 

 pletely shifted the scientific point of view as regards 

 electrical effects. What is now demanded of electrical 

 theory is an explanation of the conditions of the medium 

 which are perceptible by us as the properties of an electric 

 or magnetic field. The wider problem of the constitution 

 of the electric medium, whether identical or not with the 

 luminiferous ether, embraces in itself the phenomena of 

 electrostatics, of electric currents, and of magnetism 



There was thus every reason to wish that Prof. Wiede- 

 mann might be able to treat electrical science as a whole 

 in the same complete way in which he had previously 

 treated the portions included within the scope of his 

 previous book. This is what he has now undertaken and 

 in great part accomplished. The task is an enormous 

 one, and probably, to any one except the man who has 

 set himself to it, would have seemed overwhelming. 

 Prof. Wiedemann's industry and care, however, never 

 seem to fail before any mass of descriptive detail or 

 complex mathematical discussion, and students of physics 

 may therefore be congratulated upon the near prospect 

 of having from his pen a complete treatise on electricity. 



The first of the two volumes already published begins 

 with a section on the General Properties of Electricity, 

 including an historical sketch of early observations, the 

 development of electricity by friction, &c, electrostatic 

 attraction and repulsion, distribution on conductors, and 

 a description of the various forms of electroscopes and 

 electrometers. Then follows a section on the develop- 

 ment of electricity by contact of heterogeneous bodies ; 

 next Ohm's law and its applications, the measurement of 

 electrical resistance and of electromotive force, and a 



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