October 17. tgi8 



NATURE 



137 



B\ iln- middle of th. centur) thi Foundations ol thi 

 ci wi re well and ti ul\ laid ; its influent 1 on 

 national life had until then been but small, but the 

 ground was secured on which to build safeh the struc- 

 ture of the practical applications of electricity. In the 

 List sevent) years theon has advanced no less than 

 practice; indeed, .1- w< shall see lain, somi ol 

 tin mosl important recent practical advances an 

 tin- outcome of verj recent theory; bul the fait 

 remains that foi real progress the practical ap- 

 plication ol a science must resl upon a secure basis 

 ol theor) : onrj then will its progress l»- rapid ami 

 uninterrupted. 



Ampere's experiments and Faraday's researches had 

 indicated various methods b) which motion rc.nl, I be 

 produced owing 1.. electro-magnetic action, 01 con- 

 versely, bj which currents could be generated in con- 

 ductors moving in magnetic fields, and as a result 

 numerous inventors produced magneto machines. 

 Farada) himself used one made l>\ Pixie. In Saxton's 

 machine, employed frequentl) towards the middle ol 

 last century, two coils wound round a soft iron 

 armature rotate in front of the poles of a sfrong per- 

 manent magnet somewhat as i- done in tin- spark 

 magneto of tin- present day. 



Werner Siemens in 1857 invented tin- Siemens arma- 

 ture; tin' next step was to replace tin- permanent 

 magnets b) electromagnets, excited 03 a separate small 

 machine. Wilde's machine (1867) was of thi- class, 

 and in tlii' same year Wheatstone and Werner Siemens 

 enunciated thi- principle of tin- modern self-exciting 

 dynamo, in which the remanent magnetism of the field 

 coils is utilised to -tan a Feebli current in tin- rotating 

 armature; this current i- I'll round tin- Geld roils, thus 

 reinforcing their magnetism, and in thi- manner the 

 powerful currents generated by modem machines are 

 built up. 



So far, the fundamental principles established b) 

 Farada) had been the basis of th< work done. Various 

 distinguished men contributed 1,1 advance the theon 

 and to improve practice. About this time the I lei 

 trical Standard- Committee of the British Association 

 began its labours. Appointed at thi instanci "t Lord 

 K( Kin 1 Sir William Thomson) in 1861, during the period 

 1862 70 it made a series ol reports which have been ol 

 fundamental importance in the theor\ and practice ol 

 electricity. It was re-appointed in 1881 at the sugges- 

 tion of Prof. Ayrton, and continued to do useful work 

 until [913, when it was fell that the National Physical 

 Laboratory was carrying out thi duties for which it 

 had bei n 01 ganised. 



Lord Kelvin, in his work connected with tin- Atlantic 

 telegraph, had realised ven full) the need for con- 

 sistent system of units ol mi isurement. Such a 

 had been proposed b) Weber, and the com- 

 mittee in the end was led to adopt as fundamental 

 the 1 .G.S. (centimetre-gr; d) system of 



units, and base on ii the practical system ol electric 

 unit- tin- ohm, the ampere, and the volt now in use 

 everywhere. It is impossible erestimate the prac- 



tical effects "i this action. In the first place, elec- 

 tricians throughout the world speal .. common lan- 

 guage, and the results of researches are intelligible to 

 all .dike; in the second, that language i- a consistent 

 and logical one. electrical quanti nnected 



her and linked with the fundamental concep- 

 tion ol . nergy in the simplest manner possible, .and 

 in a wa) which permit- of accurate numerical cal- 

 culation. 



\- .. result of the labours of the distinguished 

 men who formed the commiti 



at home ami abroad, we had thi means of measuring 

 with high accuracy current, electi omotive force, and 



NO. 2555, VOL. 102] 



resistance, togethei with a number of other dependent 



electrical quan 



Anothet step wa- needed a, complete the theory of 

 the dynamo : to permit the manufacturer to design 

 on scientific principli - a machine which for a given 

 -peed of rotation would tr; n Form mechanical into 

 electrical energ) at any required rate in the form ol 

 a given current at a know 



lie- law- ol magnetit induction in iron and steel 

 were known hut verj imperfectly. As ha- alread; 

 been stated, ^rago and Daw had 1 ed in iNjo 



thai iron was magnetised by a current ; Poisson and 

 other- had given da,, lie- ol tin- induci I magnetism; 

 Kelvin in hi- earliei papers had done much 1- clear 

 up ambiguities and to give definiteness 1 ■ ■ - 1 rms 

 used. Rowland, in America, carried ottt numerous 

 experiments ol great value, hut it is to Ewing and 



Hopkinson that we owe our first real knowledge of 



the importance of the magnetisation curve, the m 

 ing of the property known as hysteresis, which had 

 a short time previously been investigated by Warbury, 



and the part this plays in the action of electrical 

 machinery. 



The experiments of Oersted and Ampere had taught 

 us that an electric current circulating in a coil of 

 wire produces a field of magnetic force linked with 

 that coil, and, as Faraday proved, the inductive effects 

 produced in any neighbouring circuit depend on the 

 manner in which that circuit is also linked with the 

 magnetic lines. 



John Hopkinson in 1S711 had shown how the pro- 

 perties of a dynamo could he deduced from its charac- 

 teristic curve, the- curve connecting the e.m.f. in the 

 armature with the exciting current in the field coil-; 

 and in a joint paper with his brother Edward, read 

 before the Royal Society in 1886, In- described how- 

 tin- form of this curve could be obtained graphically 

 for a dvnamo of known design and dimensions from 

 the ordinary law- of electro-magnetism and the known 

 properties of iron which Ewing had shown how to 

 dci. imine. The theory of the dynamo was com- 

 plete in its main outlines. Since- then progress has 

 been rapid. Theory lias indicated the direction in 

 which improvements were to be -ought; the -kill of 

 the metallurgist, tin- engineer, and the designer has 

 been called in to put those improvements int.. prac- 

 tice. 



I h.- result vou know. Conceive the world without 

 .l.ctric power — London without ii- tubes and rail- 

 ways, its electric light, telephones, telegraphs, and 

 wireless services— and you will realise to -erne degree 

 uh.,i is dui 1.. the labour- of the physicists under 

 whose skilled guidance all thi- system has grown 

 up i,, the la-t twentv-fivi 01 thirh years out of the 

 small seed -own b\ Farada) and his contemporaries. 



It i- not eas\ to obtain figures which give with 

 accuracv the extent to which electrical power i- used 

 .,, present. In the Electrical Trade- Directory for 

 ,,,,- i, i s stated that more than 500,000,000/. has 

 already been sunk in the industry, and there is every 

 prospeel oi that sum being largeh increased. 



I have endeavoured to indicate in brief outline thi 

 which this stupendous result has 

 achieved. In the- first place, we have tin disinteres 

 labours ol the man of science impelled by tin 

 I., know ; then have followed the mathematician and 

 ili.- physicist, whose work has reduced thi rly ob- 

 servations of the- experimenter to the- rul ol law, 

 and when thai law ha- been established it ha- become 

 Me for the electrical enginec rasp the 



problem and applv the lea. hie oi the physicist to 

 ih.- n.-e-ds of national lib 



Illustrations of the process, pi ■<- ol the debt dm- 



