74 



• KNOWLEDGE ♦ 



[Fed. 



1883. 



lAfblflUS!. 



ELECTRIC ILLUMINATION.* 



MR. DREDGE, one of the editors of our e.xcellent 

 contemporary Eiii/iiirrrinr/, liasaccomplislied a great 

 task in amassinr; such an amount of valuable information 

 as is to lie found in the volume now before us. The greater 

 part of it lias already appeared in the pag<!S of that journal ; 

 but tlic work involved in such a compilation brought up 

 ahncist to the day of publication, cannot have been much 

 diminished on that account. 



In a well-pointed preface, the editor is careful to warn 

 his readers against the twofold danger which must inevit- 

 ably result from such an amount of speculation as has 

 for some time been evinced by certain sections, viz., the risk 

 ignorant and gullible men run of losing their money, and 

 the reaction that must ensue, making all sections more or 

 less timid, and so hampering further discoveries and inven- 

 tions. "Possibly it will be found," says Mr. Dredge, 

 " that no mode of electric lighting can be thoroughly 

 adapted for domestic purposes until an efficient system of 

 storage batteries has been devised." Here is to be found, 

 we opine, the keystone to many a disaster that will, almost 

 beyond doubt, be witnessed before many months have 

 passed. 



We are next reminded of the fact that forty years ago 

 the attention of physicists was turned to electric lighting, 

 and that many inventors have recorded ideas in the patent 

 office, which " clash dangerously with some modern inven- 

 tions." The history of the eflbrts to make electric lighting 

 commercially successful is then briefly sketched, honourable 

 names are mentioned which we rarely hear nowadays, and 

 a useful preface is closed with an epitome of the work 

 attempted in the succeeding 900 good-sized pages. The 

 book is divided into four sections and an appendi.x. The 

 lirst section, extending over eighty-seven pages, embraces 

 five good chapters on " Electrical Units," " The Measure- 

 ment of Electrical Intensity," "The Voltaic Arc," "The 

 Mechanical Production of Electric Currents," and "The 

 Theory of Dynamo-Electric Generators " respectively. 

 The order of these chapters might, perhaps, have been 

 modified with advantage, at least as regards that 

 on " The Voltaic Arc," which occupies a somewhat 

 isolated position. The chapter on Units is admirably 

 written, the object being to convey to non-technical 

 but intelligent minds a clear conception of the prin- 

 ciples governing tlieir value and significance. We 

 notice, however, with regret, that the term '• intensity " is 

 introduced in a highly un-English, and we may add un- 

 scientific, manner. Those of our readers who have studied 

 the subject for any lengthened period will doubtless 

 remember that this term used to be applied in England in 

 the same sense that we now use the term " electro-motive 

 force." In France it has long been customary to speak of 

 " intensity " where we used to speak of " quantity," or as 

 we now say " current-strength." It is in fact the value 



" C" in the equation C=-^. There is no excuse for such 



R 

 an intrusion, the only works in which the term is similarly 

 applied being those translated from the French. The very 



* Electric Illuminatioyi. By Conrad Cooke, James Dredge, 

 M. F. O'Reilly, S. P. Thomi'son, and H. Vivarez. Edited by 

 James Dredge, with abstracts of specifications having reference to 

 electric lighting, prepared by W. Lloyd Wise, Member of Council 

 of Institute of Patent Agents. Vol. I. (London : Offices of 

 Enijineeriiuj.) 



word implies a property whicli many large currents do not 

 possess. As an illustration we may cite the Edison dynamo, 

 which, while it is capable of supplying sufficient electricity 

 to illuminate a thousand incandescent lamps, has no effect 

 whatever upon — the current cannot, in fact, pass through 

 — a human being, while tlie smaller current from a 

 Brush or any of the large dynamos for arc lighting, would 

 and has produced instantaneous death. It would, there- 

 fore, have been preferable to let the word sink into oblivion 

 rather than help to perpetuate so evident a misnomer. 

 Apart from this, the chapter may be commended as the 

 simplest and best we possess. The chapter on the voltaic 

 arc is interesting in the highest degree, and serves, too, to 

 show us how much we have yet to learn on the subject. 

 Some trouble has been taken to gather all available 

 information on the temperatm-e of the arc, which, it 

 has been said, approaches that of the sun. How varied 

 are the figures ! The highest computation for the 

 carbon is G,000° Cent., while Professor Rosetti gives 

 much lower figures. The temperature of the sun is 

 variously estimated, by Ericsson at between four and five 

 million degs. Fahr., by Secchi at 250,000° Fahr., by Violle 

 at not more than 2,500° Cent, and by Rosetti at 10,000° 

 Cent., or 20,000° if allowance is made for the absorption 

 of the solar atmosphere. The fourth and fifth chapters, in 

 which we recognise a now familiar style, very ably deal 

 with topics of the greatest importance to electricians, 

 engineers, and the public at large. " Of the thousands 

 who have heard that a steam-engine can provide us with 

 electric currents, how many are there," asks the writer, 

 " who comprehend the action of the generator or dynamo- 

 electric machine ? How many, of engineers even, can ex- 

 plain where the electricity comes from, or how the 

 mechanical power is converted into electrical energy, or 

 what the magnetism of the iron magnets has to do with 

 it all 1 " How many, indeed ! How many, may we add, 

 who imagine that friction is the source of all the mighty 

 power procured ! The way in which the difficulties are 

 gradually, progressively, and cleverly cleared away, is 

 ingenious in the extreme. 



The phraseology, however, is at times somewhat awkward 

 — as, for example, on page 51 we read, " at first it lies 

 horizontal with its plane very nearly along the lines of 

 force, so that almost none of them pass through it." These, 

 however, amid so many excellences are but slight and 

 pardonable blemishes, and we should strongly ad\"ise every 

 one who is interested in the sulrject, however expert or 

 however ignorant he may be, to carefully peruse these two 

 chapters, which close with an ingenious and well-explained 

 theory concerning the " displacement of the brushes " of 

 dynamo-machines and electric motors — a theory which may 

 be calculated to charm away many troubles in the mind of 

 the inquiring electrician. 



Section 2 is devoted to " Magneto and Dynamo-electric 

 Generators," and extends over 230 pages. Most of the 

 matter has previously appeared in the columns of Enr/ineer- 

 iiii/, but the collection of descriptions here given is of 

 extreme utility, more especially to the engineer. The 

 machines are treated historically, and every efibrt is made to 

 present a complete account of all that has been done towards 

 perfecting the dynamo. A perusal of this portion of the 

 book cannot fail to convince one of the invalidity of the 

 claims urged by numerous " inventors " of the present day. 

 The matter is carefully written, the descriptions being both 

 clear and complete. 



Section 3 deals with conductors and carbons ; the 

 chapter on conductors containing a considerable amoimt 

 of reliable information useful to the electrician and highly 

 interesting to the general reader. The relative value of 



