September 2, 1909] 



NA TURE 



•/3 



ternal affinity between hypnotism and occultism, but 

 because the two subjects are often mentioned together, 

 a connection determined by their historic develop- 

 ment. We wish that all enthusiastic investigators of 

 the occult could be induced to peruse this part of the 

 book. With a candid admission of the depth of our 

 ignorance, our author asserts that we have no right 

 flatly to refuse to recognise any domain of research. 

 Yet if the conditions of research into the phenomena 

 of occultism be severe, and if none of the assertions 

 of occultists be accepted without proof, there is, 

 according to Dr. Moll, no single series of experiments 

 that carries with it a convincing proof of the reality 

 of occultistic phenomena. We can warmly recom- 

 mend this work to our readers as a thorough exposi- 

 tion of an abstruse subject. 



ELECTRO-TECHNICS. 

 Einfiiliriing in die Elektrotechiiib. By Dr. C. 



Heinke. Pp. xviii + 501. (Leipzig: S. Hirzel, 



1909.) Price 13 marks. 

 A T a first glance this seems a very interesting 

 ■^ i- book, but a closer study of its pages produces 

 a feeling of mental fatigue, not to say impatience; 

 and this is probably due to the fact that many obvious 

 points are set out at great length whilst really 

 important or difficult matters are passed over with 

 tantalising brevity. Thus the author gives us many 

 pages on the calculation of the current in a circuit 

 containing inductance and resistance, or capacity and 

 resistance, but the subject of single-phase commutator 

 motors is dismissed in exactly two and one-third 

 pages. 



After a long-winded introduction, in which the 

 author develops his ideas as to what should be taught 

 at a technical high school and what constitutes the 

 real difference between the mere technical man and 

 the scientific engineer, we find a chapter which a 

 less pedantic writer would have simply headed 

 *' mechanical analogies," but which bears the title 

 ■" Conceptions of a Mechanical Nature to facilitate 

 the Mental Connection between all Basic Electro- 

 magnetic Phenomena." The fifty-odd pages in which 

 the author develops his analogies are very interest- 

 ing, but they can only be read with advantage by 

 persons who are already well acquainted with the 

 subject. A beginner will find the analogy more 

 difficult to understand than the electrical phenomenon 

 itself. 



Next follows a chapter entitled " Pressure Pro- 

 ducers " (German Spannungserzeuger), and in this 

 we find the old-fashioned frictional machine (but not 

 the Wimshurst), .Armstrong's experiment, primary 

 batteries, thermopiles, and the dynamic generation 

 of E.M.F. discussed. The latter leads to the follow- 

 ing chapter, on " The Technical Production of Elec- 

 trical Energy." This occupies some 200 pages, and 

 contains a most bewildering collection of all possible 

 things either directly or very remotely connected with 

 dynamos. A few titles of the matters treated will 

 suffice to show how varied is the character of the 

 subjects collected under this head : — mechanical de- 

 tails of armature ; commutator and field system ; 

 NO. 2079, VOL. 81] 



characteristics; interpoles; the Thury system as 

 applied to the Moutiers-Lyon installation ; relay for 

 field regulation ; mechanical analogy of alternating 

 currents ; a number of obsolete alternators ; some 

 modern alternators ; form factor ; oscillograms ; vector 

 diagrams ; currents in branch circuits ; resonance ; 

 stationary waves in the antenna of a wireless station ; 

 the .Slaby-Acro-Braun system of wireless ; Dobro- 

 volsky's balancing transformer for three-wire system; 

 electric bells ; Rhumkortf interrupter ; Wehnelt 

 interrupter ; selenium cell ; buzzer ; maximum cut- 

 out ; high-frequency arc ; wireless telephony ; power 

 of electric currents. 



The fifth chapter deals with the application of 

 electricity, and here we get also a great variety, such 

 as Geissler tubes, lifting magnets, bells, telephones, 

 transformers, motors, the Kjellin furnace, a cata- 

 logue picture of a chain-welding machine, glow 

 lamps, arc lamps, secondary batteries, a load diagram 

 of a central station, switchboard diagrams for D.C. 

 and A.C. stations. The final chapters deal with 

 measuring instruments, cables and overhead lines, 

 switches, and accessory apparatus. The grouping of 

 all these different matters as adopted by the author 

 may be logically right, but it is not convenient for 

 the reader; it is also irritating to find a page or so 

 of elementary mathematical treatment interleaved 

 between catalogue pictures of some firm's ap- 

 paratus, whilst the important features of the thing 

 illustrated are hardly mentioned. The book has 

 interesting parts, but to find them the reader must 

 know a good deal of the subject; and even then the 

 search will be rather troublesome, as there is no 

 index. GisBERT Kapp. 



OUR BOOK SHELF. 



(i) Lcitfaden der Tierkunde. jiir hohere Lehran- 



staltcii. Bv Dr. K. Smalian. IV. and \'. Teilen. 



(Leipzig : G. Freytag, 1909.) Price 1.80 marks 



each. 

 (2) Naturu'isseiischaftliches Unterrichtswerk fur 



hohere Mddchenschideii. Bv Dr. K. Smalian and 



K. Bernan. I. Teil. Pp. 50; illustrated. (Leipzig: 



G. Freytag, 1909.) Price 1.20 marks, 

 (i) With the two parts referred to under the title 

 of the work first quoted. Dr. Smalian brings to a 

 conclusion his " Leitfaden," of which the earlier parts 

 have been already noticed in Nature. The fourth 

 part, which is devoted to the .-Arthropoda, is stated 

 to be for lower third form teaching (Lehrstoff der 

 Untertertia), while the fifth part, dealing with the 

 other invertebrates, is intended for upper third form in- 

 struction (Lehrstoff der Obertertia). Whether the parts 

 intended for the higher forms are considered to com- 

 prise more difficult zoology than those for the lower 

 grades is not very easy to decide. As regards style 

 of treatment, the two parts before us seem to follow 

 very much the lines of their predecessors, and contain 

 a vast store of information, conveyed in a very con- 

 densed and concise manner, this technicality of the 

 text being in some degree relieved by the coloured 

 plates, the subjects of which are well selected, and 

 illustrate the life-history of a number of species. 



(2) This text-book has been written by the authors 

 in accordance with the requirements of a new scheme 

 of instruction authorised for higher grade girls' 

 schools in Prussia, and in order to conform exactly 



