442 



NA TURE 



[April 6, 1876 



" POTi NTIAL," we learn, " implies that function of 

 electricity ivhtch determines tts motion from one point to 

 another^ 



We doubt whether the eleir.entary student will obtain 

 from this definition (?) orfr^inth-i accompanying explana- 

 tions, any criterion for knowing a point of high potential 

 from a point of low potential, or any idea of how to reckon 

 numerically the potential at a ooint, or even the difference 

 of potentials between two points. 



Next we learn that " Resistance ijnplies that quality 

 of a conductor in virtue 01 which it prevents tnore than 

 a certain amount of work being d»ne in a given time by a 

 given electromotive force." This is prefaced by the extra- 

 ordinary remark that " The transference of electricity, 

 such as that from a charged cloud to the earth, from a 

 rubbed glass to a rubbed comb, a signal from Europe to 

 America, may take place in different times; the path 

 between A and B offers obstruction to the passage of 

 electricity ; the medium through which it passes ... is 

 an obstacle to be overcome." The unit of resistance is, it 

 is said, called the Ohm, tiom Ohm the German physicist, 

 but the laws of Ohm are not stated, n r is the beginner 

 even told to connect with them the idea of diminishing 

 the current bttwee*^ two points by increasing the resist- 

 ance between them ; an J with tiie exception of the mys- 

 terious and inaccurate reference to work done, just quoted, 

 (and the work done in the circuit by no means presents 

 itself directly to the attention of the beginner in electrical 

 studies), there is nothing to afford a clue to the effect of 

 tie resistance in a given circuit. This remarkable chapter 

 concludes as follows : — 



" The nature of electricity itself is not known, nor is 

 it necessary to the telegraphist that it should be known 

 by him. He is only interested in its quantitative mea- 

 surement and it-, apnlication to practical purposes. Let 

 him naster its elementary principles, its general ideas, its 

 propel ties and ts conditions, and he can well afford to 

 leave to physicists the discussion of its nature, and to 

 mathematii,» < ns the determinaf'on of its laws." 



We have no objection to these general sentiments, but 

 we venture to think that for any one who wishes to write 

 a book on telegraphy a moderate amount of attention to 

 what the naLuralist ^ we can't call him physicist) and mathe- 

 matician have to impart would not be out of place. 



We are far from satisfied with the chapter on bat- 

 teries and with the ch; ^ters on construction ; in fact our 

 idea of what the artisan class and the beginners in science 

 schools should expect to learn from a text-book of science 

 in no way agrees with the ideas of the authors of this 

 book. We cannot think that the last chapter (fifteen 

 pages), describing the message-forms used in the British 

 postal telegraphs, and a mass of technicalities even to the 

 inserting of the received message in an envelope and 

 handing it to the messenger, will be of use to anyone. 

 And yet the dimensions allowed for the book have com- 

 pelled the auth«rs, as they tell us, " to abandon the sub- 

 marine cable branch of the subject" ! Similarly, " quad- 

 ruplex, multiplex, and other novel systems of telegraphy 

 have been omitted." ..." The discussion of Ohm's laws 

 and the apparatus depending upon them are not dealt 

 with." Everything scientific is in fact left out. 



There is a mass of technicality in the chapter on 

 batteries, of which a host are described with their prices. 



&c. If space were of no consequence this would be 

 most interesting but, for want of space, we presume, the 

 principles of testing batteries for electromotive force and 

 resistance are omitted. The chapters on construction 

 contain elaborate discussions as to charring, tarring, bur- 

 netising, kyanising, boucherising poles, about the relative 

 merits of different kinds of wood, about earth-borers, and 

 a multitude of other things, while the principles of the 

 parallelogram of forces practically applied to the fixing of 

 poles by stays and struts are not mentioned. We should 

 have thought that Mr. Preece, Mr. Sivewright, and their 

 coadjutors leave but little choice to the artisan as to the 

 materials and the tools to be employed in construc- 

 tion of telegraph lines, and that practical application of 

 the science of dynamics to the case in hand would be of 

 far higher value to the man who is actually engaged in 

 stepping the poles and fixing the stays and struts, than a 

 not very perfect description of the methods adopted for 

 the preservation of timber. The gauge of the iron wire 

 employed in Post Office Telegraphs is given. We are 

 left to wonder whether in selecting wire any test as to 

 electric resistance is applied or not ; and we are not told 

 what kind of preliminary electrical test, if any, ought to 

 be applied. In fact, though these questions are intrinsi- 

 cally of extreme importance, they ought not to have been 

 allowed utterly to displace the fundamental principles of 

 the science of telegraph construction and of telegraphy. 

 While they form a part of the whole subject, and they do i 

 form a very important part of it, they should have occu- I 

 pied a subordinate place in a book for beginners. Those j 

 who want an elementary text-book on the science of tele- ! 

 graphy, want more than a description of the practice, on 

 their land lines, of the British Postal Telegraph depart- 

 ment. 



The chapters taken up with the instruments are, in our 

 opinion, the best part of the book. The instruments used j 

 on land-lines are well described. Interesting information \ 

 is given as to rates of working. Some of these show very j 

 wonderful results of practice. For example we learn that i 

 an experienced operator usually punches forty-five words I 

 per minute. Now a word contains 4*5 letters, and if we 

 take it that an average letter contains, including the space ; 

 that divides it from the next letter, four dots, we find \ 

 that at this rate of punching ly^ dots per second are| 

 made. If three more dots could be made per second, the' 

 strokes with the mallets would nearly cease to be heardj 

 distinct one from the other, and a deep musical note four; 

 octaves below the middle C on the pianoforte would be I 

 the result. We wonder whether this could be done were I 

 the operator to punch a few times over some sentencej 

 that he knows by heart. 



We have noticed in reading the book some errors tb 

 it would be well to correct in future editions. On p. 21, 

 damp ground is said to abstract a certain portion of thej 

 current. On p. 32, a battery is described as Thomson's.! 

 which is not used, and never was used, except for an 

 experiment. Sir W. Thomson has arranged a gravit)| 

 battery, very different in form from that here described 

 and which, being in use with his Siphon recorder, i: 

 generally known as his battery. In figures 69 and 93 th' 

 battery is represented as short-circuited by the sendi 

 key. On the whole, however, the diagrams are clear, ai 

 descriptions of the instruments well written. 



