November 29, 1895.] 



SCIENCE. 



73T 



Encyclopffldists (It is difficult to imagine them 

 to be anything else than yovithful, no matter 

 how many years they may have lived), will 

 hold themselves in check until they learn some- 

 thing that other people do not know, or until 

 they learn what other people do know so well 

 and so clearly that they can claim some right 

 to classify, edit and arrange existing knowledge, 

 they will confer a favor upon themselves the mag- 

 nitude of which it is difficult to estimate. 



Alternating Electric Currents. By Edwin J. 

 Houston and A. S. Kennelly. New York, 

 The W. J. Johnston Co. Pp. 225. Price $1. 

 This little volume forms one of the ' ' Electro- 

 Technical Series," of Avhich nearly a dozen vol- 

 umes have been prepared by Messrs. Houston 

 and Kennelly. It treats of one of the most 

 important and most prominent departments of 

 applied electricity. The development of the 

 theory of Alternating Currents and their prac- 

 tical utilization is of comparatively recent date. 

 The large pecuniary interests involved in the 

 variovis processes by which energy is trans- 

 formed have put a premium upon the explo- 

 ration and exploitation of this branch of physical 

 science such as no other has ever felt. Workers 

 in science generally are sustained by that motive 

 and inspiration which compels the practical 

 geographer to force his way into and through 

 unknown regions, his reward being the knowl- 

 edge of their nature and inhabitants, with which 

 he is laden when he returns. In electricity 

 there is the additional powerful incentive that 

 gems and precious metals are tolerably sure to 

 be met with. The science of electricity has 

 prospered, therefore, during the last decade in 

 a manner only equaled or excelled by its prac- 

 tical applications. Even the expert now finds it 

 difficult to keep thoroughly informed of the 

 rapid and often far-reaching advances that are 

 continually being made. To the layman, or even 

 to the general physicist, who has not been forced 

 as, alas ! nearly all have, to ' specialize ' in 

 electricity, any book which summarizes this 

 progress in an intelligent and scientifically cor- 

 rect manner will be welcome. To such this 

 book will be of much use. The conception of 

 the alternating current is well worked out in 

 the first chapter, and in those following its ap- 



plication to the transmission of power and to 

 electric lighting is discussed in a popular read- 

 able form, including a discussion of diphase, 

 triphase and monocyclic currents and transmis- 

 sion. The principle criticism that may be 

 applied to the book is the unnecessary presen- 

 tation of a great deal of elementary matter, 

 concerning which the reader is almost sure to 

 be already well informed. It does not seem 

 likely that any one who undertakes to read a 

 book, be it ever so simple, on 'Alternating 

 Electric Currents' will be entirely ignorant of 

 a simple primary battery, of the form of an 

 electric magnet, of the appearance and construc- 

 tion of an incandescent lamp, of which there is 

 a long and elaborate description. The amount 

 of ignorance which is here assumed is not quite 

 in harmony with the amount of technical infor- 

 mation which the reader must possess in order 

 to understand other portions of the book. The 

 volume could have been made more valuable 

 by assuming on the part of the reader that 

 knowledge of direct current electricity which 

 he is tolerably certain to possess or which he 

 can readily obtain from other volumes of the 

 same series. There are certain advantages, it 

 is true, in having each volume complete in it- 

 self, but these are greatly exceeded by the dis- 

 advantages growing out of the enforced buying, 

 owning and reading the same matter over and 

 over again. 



THE MAGNETIC EESURVEY OF AUSTRIA AND 

 HUNGARY. 



From a recent report* by Dr. Lizuar, of 

 the ' Central Anstalt fiir Meteorologie und Erd- 

 magnetismus ' of Vienna, we find that the re- 

 cent magnetic resurvey of Austria and Hun- 

 gary (1889-93) has been brought to a termina- 

 tion. An earlier magnetic survey had already 

 been made by Karl Kreil between the years 1843 

 and 1858, which was repeated a few years later, 



*J. Liznar: Die Vertheilung der erdmagnetischen 

 Kraft in Osterreioh-Ungarn zur Epoche 1890.0 nach 

 den in den Yahren 1889 bis 1891 ausgefiihrfcen JVIes- 

 sungen. 1 Theil, Erdmagnetische Messungen in Os- 

 terreich ausgefiihrt auf Kosteu d. Kais. AkadJ d. 

 Wiss. in d. Y. 1889-'93, von. J. Liznar. Wien, 1895, 

 4°, 232 pp. Repr. Denk. d. Wiener Akad. Math, 

 naturw. CI. Bd. LXII. 



