NATURE 



529 



A "PRACTICAL MAN'' ON ELECTRICAL 

 UNITS. 



AT the last meeting of the British Association an 

 energetic attempt was made to prove that the pro- 

 gress of the human race has been chiefly due to the 

 "practical man," and this teaching was quickly caught 

 up and explained to mean that the triumphs of industry 

 have been achieved without the help" of workers in the 

 field of pure science. We have before us a periodical 

 which is instructive reading when viewed in the light of 

 the discussion on this subject. It is a recently issued 

 number of the Transactions of an Institute connected with 

 one of the most important of our national industries. 

 Among other provincial organizations it holds high rank. 

 Meetings are held at frequent intervals, papers are read, 

 and not only are they printed at length, but the dis- 

 cussions by which they are followed are also given in full. 

 Two papers were recently communicated to this Society 

 on the apphcation of electricity to the industry with which 

 its members are chiefly connected. One of them was by a 

 gentleman who, according to the Chairman, represented 

 an important firm " who have done more of this class of 

 work in this country than anyone else," and he added 

 that on this account " anything that he may say will 

 carry great weight and g^ve information to us unattain- 

 able otherwise, and I am sure we shall therefore appre- 

 ciate the more, the trouble he has been at in coming 

 here." The whole of the last number of the Transactions 

 of the Institute — forty-one pages in all — is filled with the 

 discussion that followed the speech in which this passage 

 occurred. 



We give these details because we wish to make it clear 

 from the loutset that the thing which we are about to 

 discuss was not done in a corner. No circumstance 

 which could add to the formality and importance of the 

 occasion was wanting. A full account of the whole is 

 published, and is matter for public comment. 



Let us now see how the gentleman thus introduced 

 and who calls himself a practical man utilized this oppor- 

 tunity. In the course of his remarks he discussed the 

 theory of the electric motor, and then proceeded to say 

 that he was frequently asked 



"why we measure electrical quantities in volts, amperes, 

 and watts, rather than in foot-pounds. Well, the main 

 reason is that the practical units, the volt, ampere, and 

 ohtn, are so easy to measure and so simply connected by 

 the equation 



in which C = the ampere, the unit of current ; 



E = the volt, „ „ pressure ; 



R = the ohm, „ „ resistance. 

 Now, the product of one ampere and one volt = one 

 watt, and 746 watts = one horse-power. 



" In the mechanical units 33,000 foot-pounds = one 

 horse-power per minute ; and if we are doing electrical 

 work at the rate of 746 watts per minute, we are doing 

 33,000 foot-pounds per minute. The electrical unit of 

 work is then related to the mechanical unit by the ratio 



- 74 Qj. Qjjg ^^if ig equal to 4*4 foot-pounds. 

 33,000 ^ 



Vol. xxxix.— No. 1014. 



"We could thus measure all electrical quantities in 

 foot-pounds if it were desirable, but it is far more con- 

 venient to measure the volts and amperes, and then 

 estimate the horse-power. If anyone, however, wishes to 

 express electrical quantities in foat-pounds, he will now 

 be able to do so ; but bear in mind that the electrical 

 horse-power is equal to the mechanical brake horse- 

 power." 



It is hardly necessary to point out the blunders with 

 which every sentence of this passage teems, but it is 

 necessary that they should be made evident to "prac- 

 tical men." To talk of measuring a volt or an ampere 

 in foot-pounds is as ridiculous as to propose to measure 

 miles or gallons in seconds ; and yet, when the inquirer 

 asks why it is not done, he is told that " all electrical 

 quantities could be measured in foot-pounds if it were 

 desirable." 



In the equation C = E/R, the symbols, when applied 

 to the practical system of units, do not represent the 

 ampere, volt, or ohm, but certain numbers of amperes, 

 volts, and ohms. 



The " horse-power per minute " is an old friend ; it has 

 as much meaning as the statement that a man has walked 

 four miles per hour per second. Of course, the equally 

 absurd phrase " watts per minute " follows. 



Next, we find the " electrical unit of work " confounded 

 with the unit of power, and the statement that their ratio 

 is 746/33000 ; the truth being that the ratio between the 

 watt and the horse-power is i : 746. As the first of these 

 fractions is nearly seventeen times greater than the 

 second, this sentence, in so far as it means anything, 

 makes the watt seventeen times too great. 



Lastly, like a cockney, who, having put in unnecessary 

 ^'s, proceeds to redress the balance by leaving them out 

 where ordinary mortals insert them, the speaker, having 

 liberally distributed " per minute " where it makes non- 

 sense, proceeds to leave it out where it is absolutely 

 necessary. The statement that " i watt is equal to 4*4 

 foot-pounds " is wrong, (i) because the ratio of 33,000 to 

 746 is 44, and not 4*4 ; (2) because it is necessary to add 

 " per minute " after " foot-pounds." The " practical 

 man " of this type apparently thinks that it is quite unim- 

 portant whether a machine does 44 foot-pounds of work 

 in a second, or in a minute, or in all eternity. 



In drawing attention to this extraordinary series of state- 

 ments, it is necessary to point out that nobody desires 

 to interfere with such engineers provided they confine 

 themselves to fulfilling the useful function of putting to- 

 gether machines they do not understand, and learning 

 by bitter experience, but, be it well understood, at other 

 people's expense, practical wrinkles which may no doubt 

 often be of great service. 



When, however, they pose as electricians, go down to 

 the provinces as instructors of the ignorant, and print 

 their opinions on " Sir William Thompson's " {sic) ad- 

 dress to the Institute of Electrical Engineers, the matter 

 becomes serious. 



The speech from which we have quoted was charac- 

 terized as "clear and explicit." A "junior member of 

 the Institute enjoyed this lecture more than any we have 

 had since I have joined," and thought that " we have had 

 a very instructive meeting." 



Thus these guileless representatives of a great British 



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