NA TURE 



441 



THURSDAY, APRIL 6, 1876 



PREECES TELEGRAPHY 



Telegraphy. By W. A. H. Preece, C.E., Divisional Engi- 

 neer, Post Office Telegraphs ; and J. Sivewright, M.A., 

 Superintendent (Engineering Department) Post Office 

 Telegraphs. (London : Longmans, Green and Co., 



1876.) 



IT is with feelings of great disappointment that we lay 

 down the latest book on Telegraphy. In a work 

 professedly a text-book of science, one of the series that 

 contains Clerk Maxwell's Heat, Jenkin's Electricity, Good- 

 eve's Mechanism, and the books of Bloxam and of Miller, 

 we certainly were not prepared to find the part of science 

 consistently left out. We considered, in fact, that when 

 two authors, high in their profession, undertook to supple- 

 ment a recognised want in so distinguished a series of 

 text-books, we might expect to receive from them the best 

 and the newest information obtainable on the subject that 

 they profess to deal with. 



In the last twenty years the advances in our knowledge 

 of the. science of electricity and magnetism and of the 

 principles of telegraphy, a branch of electrical science 

 applied, have been very great and very important. The 

 science and the practical application of electricity have 

 occupied a large part of the attention of the foremost inves- 

 tigators in physical science. The labours of Gauss, Weber, 

 Faraday, Joule, Helmholtz, Thomson, Maxwell, and of the 

 celebrated British Association Committee on Standards 

 of Electric Resistance have given to the student on the 

 one hand and to the practical engineer on the other, a 

 system of laws, of methods of calculation, and of experi- 

 mental results as to properties of matter, that make the 

 science of electricity perhaps the most exact of all the 

 branches of Natural Philosophy. To ignore every exact 

 principle from first to last of a science so well founded, 

 and to substitute for a clear statement of these well- 

 known principles a few sketchy paragraphs not worthy of 



J middle of last century, is not, in our opinion, the 



oper introduction to a scientific text-book on Telegraphy 



: beginners. 



The authors of the work before us naturally think that 

 " Electricity being its main theme a certain acquaintance 

 with the elementary principles of that science must be 

 assumed on the part of the reader." However, "the 

 differences which exist among electricians with respect to 

 the signification of many of the technical terms employed 

 in connection with telegraphy render it necessary that the 

 student at the outset should have a clear comprehension 



I of the meaning of those which will be used in this work." 

 Accordingly they proceed to give him a " clear" idea of 

 " Electric quantity," " electric potential," " electric re- 

 sistance " in the following way : — 



'• Electricity is an agent pervading terrestrial and solar 

 space, and is as universal in its effects as are heat and 

 light. We are cognisant of its existence when we hear 

 the roar of thunder and see the flash of lightning, but we 

 do not know its particular form any more than we know 

 ;that of heat or that of light. The sound of the thunder 

 land the flash of the lightning affect the ear and the eye — 

 ! Vol. xiii.— No. ^;6 



we hear the sound and see the light — but we do not 

 assume the existence either of sound or of light as distinct 

 entities or things [Remarkable statement]. We can 

 speak of the quantity of sound caused by the explosion of 

 a cannon or by the blowing of a penny whistle, th e quan- 

 tity of light emitted by a gas jet or by a farthi ng rush- 

 light ; the quantity of heat required to melt a p ailful of 

 ice or to solder a metal joint, without implying by the 

 term quantity a mass or volume of anything actually 

 present." 



Notions such as these as to quantity are quite new to 

 us. We would suggest as an examination question for 

 science classes the comparison of the quantity of sound 

 caused by an explosion with the quantity caused by blow- 

 ing a penny whistle for a week. 

 Our authors proceed : — ■ 



" The term implies relative magnitude only. It is the 

 answer to the question, ' How much ? ' It implies the 

 notion of more or less. When we speak of the magni- 

 tude of electricity present or passing, we speak of its 

 quantity. When we read of the church spire destroyed, 

 ot trees riven to spHnters, of wires fused, or of flocks 

 killed, the damage done is due to the electricity passing, 

 and the amount of that damage is proportional to its 

 magnitude or quantity. If we take a piece of sealing- 

 wax, a glass rod, or an ebonite comb, and rub it against 

 the coat-sleeve, we find it has the property of attracting 

 feathers, straws, and other light bodies. Electricity has 

 been excited upon its surface, and the force of attraction 

 is found to increase with the quantity of electricity 

 present. Conversely the force with which bodies are 

 attracted is an indication of the quantity of electricity 

 excited. Hence we learn that electric quantity is 

 the magnitude or amount of electricity present." 



The italics and capitals in all the quotations are due 

 to the authors. 



With no further explanation or hint of anything more 

 definite, but with a few lines, apparently meant for an 

 explanation of the algebraic method of representing num- 

 bers by letters, the authors calmly remark : — 



"The unit quantity of electricity in general use has 

 been called a weber, from Weber, one of the great Ger- 

 man philosophers." 



This is absolutely everything that is given to the ele- 

 mentary student to enable him to understand what is 

 meant by quantity of electricity. Not a single experi- 

 ment is described, except the electrostatic experiment of 

 rubbing a glass rod, an experiment which has very little to 

 do with the electromagnetic unit of quantity, the weber. 

 Not a hint is given of the electromagnetic, electro- 

 chemical, or thermal effects of the current. We can 

 picture to ourselves a student of lively imagination in sad 

 perplexity as to whether the unit of current is to be ex- 

 pressed in terms of trees destroyed or of church-spires 

 smashed per second, and as to the numerical relation 

 between unit damage done and the weber. All this in 

 the face of the beautifully simple absolute system of elec- 

 trical measurement now universally adopted I 



Space does not permit us to transfer to our pages in 

 fuU the notions of the authors on other fundamental ques- 

 tions, though some of them are not less important than 

 that which has just been noticed. A few lines of quota- 

 tion must suffice. 



