630 



N.A TURE 



[Oct. 30, ii 



removalof an untrustworthy system of defence, materially 

 added to our national safety against the importation of 

 infection. 



The second question which suggests itself is : — What 

 are the cholera prospects for Europe and this country 

 during 1885 ? This question is one which it is by no 

 means easy to answer, for to a great extent it must neces- 

 sarily depend on the action that may have been and still 

 will be taken for the removal of the conditions winch 

 are favourable to the diffusion of cholera. From the 

 middle of 1865 to the beginning of 1869 there was 

 probably no time when Europe could be regarded as free 

 from the disease, and it was doubtless only a recrudescence 

 of the same disease that led to the five years' outbreak 

 which, commencing during the summer of 1S69, was 

 destined to prevail in one or other part of Europe up to 

 1874. Or to take individual countries and towns. Accord- 

 ing to the report of the late Mr. Netten Radcliffe, all the 

 Italian provinces which suffered from cholera in 1865, with 

 three exceptions, were again affected in 1S66 ; the epidemic 

 culminated in 1 867, and only came to an end in January 1 868. 

 Again, the disease was more extensively diffused through 

 France in 1866 than even in 1S65 ; in 1867 it continued 

 in departments previously infected, and it reappeared in 

 some where it had ceased. In the province of Naples, 

 cholera, commencing in 1S65, did not cease until 1867. 

 But fortunately such maintained and recurring prevalences 

 are not the invariable rule, and even the last Neapolitan 

 epidemic of 1873 was of much shorter duration than the 

 earlier ones had been. The common theory that a 

 cholera outbreak in one year is almost certain to be followed 

 by a second one the next year is not a law of epidemics ; 

 the fact is rather due either to the failure to remove 

 infected matter left over from the first epidemic, or, as in 

 the case of England in 1865-66, to fresh importation of 

 infection. In brief, it is the sanitary state of Naples, 

 Spezia, parts of Toulon and Marseilles, and such like 

 places, that mainly affords grounds for the fear that no 

 intervention of winter weather can, apart from the adop- 

 tion of sanitary measures on a wide scale, free the infected 

 places from a contagium which, if left behind, may renew 

 its activity next season. On the other hand, the mainten- 

 ance of conditions of wholesome cleanliness should give a 

 guarantee that even a fresh importation may fail to spread. 

 Numerous importations took place into this country in 

 1873, an< i a " proved abortive. Our sanitary authorities 

 can insure a like success in 1885, even if the disease be 

 either maintained or reappear next year in Southern 

 Europe. 



DYNAMO-ELECTRIC MACHINERY 



Dynamo-Electric Machinery. By Prof. Silvanus P. 



Thompson. (London: E. and F. N. Spon, 1884.) 

 pROF. SILVANUS P. THOMPSON has undertaken 

 the task of filling up a most important want in our 

 scientific and technical literature ; and he is to be con- 

 gratulated and warmly thanked for the manner in which 

 the task has been performed. Of the want of a scientific 

 and practical work on dynamo-electric machinery there 

 can be no question. The subject is at present exciting 

 more general attention than was, perhaps, ever before 

 given to any invention, not even excluding the steam- 



engine or the electric telegraph. The electric light effects 

 are fascinating to a degree ; and in these days of exhi- 

 bitions and displays the natural interest in one of the 

 most beautiful inventions has been fostered even beyond 

 that which is natural : while speculation and even the 

 promises of "electric light in our homes "have led to 

 excitement which has been equally disastrous to the hopes 

 of the many and to the progress of electric lighting itself. 

 We are now entering it is to be hoped, or indeed have 

 already entered, upon a more satisfactory state of things, 

 in which hard and steady work and careful scientific 

 investigation of every point on which efficiency and 

 advantage in electric lighting depends will quietly bring 

 forth an appropriate reward ; and will gradually sweep 

 away the painful impressions left by the failures of 

 would-be electricians and of bubble companies. 



Information on the subject of dynamo-electric ma- 

 chinery up to the present time has been very much 

 diffused and not convenient for access, and there was 

 great need of a careful hand to bring together as much ot 

 it as was really valuable. It consisted chiefly of a multi- 

 tude of articles in the two English and two or three 

 foreign electrical journals, and a few papers to the 

 learned societies, generally on some special class of 

 machine. Of English books we have scarcely any of 

 importance except those of Mr. James Dredge and of Mr. 

 J. E. H. Gordon, useful in their way as very handsome 

 picture-books, and the former affording admirable de- 

 tailed and figured diagrams, and a complete list of the 

 legion of recent electric patents. A book of moderate 

 dimensions, and written from a scientific point of view, 

 will be welcomed alike by practical men and by theoreti- 

 cal students of this subject. 



In Prof. Thompson's " Dynamo-Electric Machinery " 

 we find, in five preliminary chapters, a satisfactory de- 

 scription of the properties of the magnetic field and of the 

 effect of moving a coil within it ; of ideal simple dynamos 

 of different forms, accompanied by curves showing the 

 electromotive forces produced by the rotation of rudi- 

 mentary coils, the effect of superposition of electromotive 

 forces, and the effect of the commutator. The series 

 dynamo, shunt dynamo, and the compound-wound dy- 

 namo are likewise described in simplified form in these 

 preliminary chapters, and likewise the various effects of 

 electro-magnetic induction ; and from these preliminary 

 remarks there follows a long list of practical conclusions. 



Chapter VI. is devoted to the government of dynamos, 

 a subject which has engrossed a large share of the atten- 

 tion of practical inventors during the last four or five 

 years. So long as electric lighting was carried on with 

 arc lamps alone, and when the arc lamps were so imper- 

 fect as they were at that period, irregularities in the action 

 of the dynamo machine were little noticeable in compari- 

 son with the irregularities of the arc itself. The use of 

 the incandescent lamp, however, soon made these irregu- 

 larities only too apparent ; and attempts to rectify this 

 defect in the dynamo have given rise to improvements of a 

 very substantial character, not only as to regularity but in 

 economy, and also in other and less important matters. 



Following these preliminary chapters we find a very 

 full and very interesting description of all the really im- 

 portant existing dynamos, with an account of their pecu- 

 iarities and of the purposes for which each is specially 



