August 15, 1907] 



NA TURE 



595 



construction, which has been ever since in general use 

 to make the principle plain. The counter-electromotive 

 force generated by the motor when running, which Hunt 

 and Tyndall deplored as a defect, is the very thing which 

 enables the motor to appropriate and convert the energy 

 of the battery. Its amount relatively to the battery's own 

 electromotive force is the measure of the degree to which 

 the energy which would otherwise be wasted as heat is 

 utilised as power. Pure science stepped in, then, to con- 

 firm the possibility of a high efficiency in the electric 

 motor ficr se. But pure science was also brought into 

 service in another way. .\n old and erroneous notion, 

 which even now is not quite dead, was abroad to the 

 effect that the best way of arranging a battery was so to 

 group its component cells that its internal resistance should 

 be equal to the resistance of the rest of the circuit. If 

 this were true, then no battery could ever have an efficiency 

 of more than 50 per cent. It was supposed in many 

 quarters that this misleading rule was applicable also to 

 the dynamo. The dynamo makers discovered for them- 

 selves the fallacy of this idea, and strove to reduce the 

 interna! resistance of the armatures of their machines to 

 a minimum. Then the genius of the lamented John 

 Hopkinson led him to apply to the design of the magnetic 

 structure of the dynamo abstract principles upon which 

 a rational proportioning of the iron and copper could 

 result. .\ similar investigation was independently made 

 by Gisbert Kapp, and between these accomplished engineers 

 the foundations of dynamo design were set upon a scientific 

 basis. To the perfection of the design the magnetic studies 

 of our ex-Prcsident, Prof. Ewing, contributed a notable 

 part, since they furnished a basis for calculating out the 

 inevitable losses of energy in armature cores by hysteresis 

 and parasitic currents in the iron when subjected to re- 

 curring cycles of magnetisation. Able constructive 

 engineers. Brown, Mordcy, Crompton, and Kapp, perfected 

 the structural development, and the dynamo within four 

 or five years became, within its class, a far more highly 

 efficient machine than any steam engine. And as by the 

 principle of reversibility every dynamo is also capable of 

 acting as a motor, the perfection of the dynamo implied 

 the perfection, both scientific and commercial, of the motor 

 also. The solution in the 'eighties of the problem how to 

 make a dynamo to deliver current at a constant voltage 

 when driven at a constant speed, found its counterpart 

 in the solution by Ayrton and Perry of the corresponding 

 problem how to make a motor which would run at constant 

 speed when supplied with current at a constant voltage. 

 Both solutions depend upon the adoption of a suitable com- 

 pound winding of the field magnets. 



.A little later alternating currents claimed the attention 

 of engineei's ; and the alternating . current generator, or 

 " alternator," was developed to a high degree of perfec- 

 tion. To perfect a motor for alternating currents was not 

 so simple a matter. But again pure science stepped in, 

 in the suggestion bv Galileo Ferraris of the extremely 

 beautiful theorem of the rotatory magnetic field, due to 

 the combination of two alternating magnetic fields equal 

 in amplitude, identical in frequency and in quadrature in 

 space, but differing from each other by a quarter-period 

 in phase. To develop on this principle a commercial 

 motor required the ingenuity of Tesla and the engineering 

 skill of Dobrowolskv and of Brown : and so the three- 

 phase induction motor, that triumph of applied science, 

 came to perfection. Ever since 1891, when at the Frank- 

 fort Exhibition there was shown the tour dc force of 

 transmitting 100 horse-power to a distance of 100 miles 

 with an inclusive efficiency of 73 per cent., the commercial 

 possibility of the electric transmission of power on a large 

 scale was assured. The modern developments of this 

 branch of engineering and the erection of great power- 

 stations for the economic distribution of electric power 

 generated by large steam plant or by water-turbines are 

 known to all engineers. The history of the electric motor 

 is prolmbly without parallel in the lessons it affords of the 

 commercial and industrial importance of science. 



But the query naturally rises : If a steam-engine is still 

 needed to drive the generator that furnishes the electric 

 current to drive the motors, where does the economy come 

 in ? Why not use sinall steam-engines, and get rid of 

 all intervening electric appliances? The answer, as every 



NO TQ72, VOL. 76] 



engineer knows, lies in the much higher efficiency of large 

 steam-engines than of small ones. A single steam-engine 

 of 1000 horse-power will use many times less steam and 

 coal than a thousand little steam-engines of i horse- 

 power each, particularly if each little steam-engine re- 

 quired its own little boiler. The little electric motor may 

 be designed, on the other hand, to have almost as high an 

 efilciency as the large motor. .\nd while the loss of energy 

 due to condensation in long steam-pipes is most serious, 

 the loss of energy due to transmission of electric current 

 in mains of equal length is practically negligible. This 

 is the abundant justification of the electric distribution of 

 power from single generating centres to numerous electric 

 inotors placed in the positions where thev are wanted to 

 work. 



Education and Training of Engineers. 

 Interplay of action and reaction make for progress not 

 only in the evolution of the scientific industries, but also 

 in the development of the individual engineer. In him, 

 if his training is on right lines, pure theory becomes an 

 aid to sound practice ; and practical applications are con- 

 tinually calling him to resort to those abstractions of 

 thought, the underlying principles, which when known 

 and formulated are called theories. Recent years have 

 brought about a so much belter understanding of educa- 

 tion, in its bearing upon the professions and constructive 

 industries, that we now seldom hear the practical man 

 denouncing theory, or the theorist pooh-poohing practice. 

 It is recognised that each is useful, and that the best 

 uses of both are in conjunction, not in isolation. As a 

 result of this better understanding distinct progress is 

 being made in the training of engineers. Of this the 

 growth of the engineering departments of the universities, 

 and of the technical colleges and schools, affords striking 

 evidence. The technical schools, moreover, are recognising 

 that their students must have a sound preliminary educa- 

 tion, and are advancing in the requirements they expect of 

 candidates for admission. They are also finding out how 

 their work may best supplement the practical training in 

 the shops, and are improving their curricula accordingly. 

 In the engineering industry, too. Great Britain is slowly 

 following the lead taken in .America, Germany, and 

 -Switzerland, in the recognition afforded to the value of a 

 systematic college training for the young engineer, though 

 there is still much apathy and even distrust shown in 

 certain quarters. Vet there is no doubt that the stress of 

 competition, particularly of competition against the indus- 

 try and the enterprise of the trained men of other nations, 

 is gradually forcing to the front the sentiment in favour 

 of a rational and scientific training for the manufacturer 

 and for the engineer. As William Watson, in his " Ode 

 on the Coronation," wrote in a yet wider sense of 

 England :> — 



For now the day is unto then that Icnow, 



And not henceforth she stumble-J on the prize : 



And yonder march the nations full of eyes. 



Already is doom a-spinning. . . . 



Truly the day is " unto thein that know." Knowledge, 

 perfected by study and training, inust be infused into the 

 experience gained by practice : else we compete at very 

 unequal odds with the systematically trained workers of 

 other nations. Nor must we make the mistake here in 

 the organisation of our technical institutions of divorcing 

 the theory from its useful applications. In no department 

 is this more vital than in the teaching of mathematics 

 to engineering students. For while no sane person would 

 denv that the study of mathematics, for the sole sake of 

 mathematics, even though it leads to nothing but abstract 

 mathematics, is a high and ennobling pursuit, yet that 

 is not the object of inathematical studies in an engineering 

 school. The young engineer must learn mathematics not 

 as an end in itself, but as a tool that is to be useful to 

 him. And if it is afterwards to be of use to him, he must 

 learn it by using it. Hence the teacher of mathematics 

 in an engineering school ought himself to be an engineer. 

 However clever he be as a mathematical person, his teach- 

 ing is unreal if he is not incessantly showing his learners 

 how to apply it to the problems that arise in practice ; 

 and this he is incapable of doing if these problems do 

 not lie within his own range of experience and knowledge. 

 Were he a heaven-born senior wrangler, he is the wrong 



