November 6, 1919] 



NATURE 



239 



Every day we are learning more of the nature 

 and properties of the various kinds of X-rays, the 

 50ft and hard primary rays, the homogeneous and 

 other secondary rays ; and knowledge is increas- 

 ing regarding their action on the surface and 

 within the body tissues. 



It is safe to predict that in the coming years 

 X-rays will play an increasingly important part in 

 attaining the end and aim of all medical study — 

 the prevention of disease arid the maintenance of 

 a high standard of health and efficiency in the 

 community. 



PROGRESS OF ELECTRICAL INVENTION. 



By Prof. J. A. Fleming, F.R.S. 



THE progress of electrical discovery and in- 

 vention, and especially of electric lighting, 

 telegraphy, and telephony, in the last fifty years 

 is the theme on which the Editor of Nature has 

 asked me to make a short contribution to this 

 jubilee issue. The chief difficulty, however, is 

 in selecting from the enormous stores of accumu- 

 lated knowledge the topics most worthy of notice 

 in a space all too brief for anv adequate treat- 

 ment. 



Casting our glances backward to 1869, we can, 

 however, say that on the theoretical side elec- 

 trical science was then beginning to emerge from 

 the stage of a chiefly qualitative study of pheno- 

 mena into an era of quantitative measurement, on 

 which progress .so much depends. The initial 

 attempts to lay deep-sea submarine cables and the 

 engineering aspects of land telegraphy had com- 

 pelled attention to the exact measurement of elec- 

 trical quantities. Advanced physicists had already 

 appreciated the advantages of an absolute system 

 of measurement based on the fundamental units 

 of space, time, and mass ; but practical elec- 

 tricians still employed vague phrases such as 

 "quantity currents" and "intensity currents," 

 and precise ideas on the subjects of potential, 

 capacity, inductance, electric energy, and power 

 were not widely diffused. Lord Kelvin (then 

 Prof. W. Thomson) had, indeed, started into 

 existence some years previously (in 1861) the 

 famous British Association Committee on Elec- 

 trical Units, and Maxwell, Balfour Stewart, and 

 Fleeming Jenkin had commenced experiments on 

 the practical determination of the ohm, or British 

 Association unit of electric resistance, for which 

 work Faraday, W. Thomson, and Maxwell in 

 Great Britain, ;md Ciauss, \\'eber, and Helmholtz 

 in flermaiiy had laid the foundations. 



A new era began in 1873 with the publication 

 of Maxwell's stimulating work on electricity and 

 magnetism. Up to that time students of the 

 subject for the most part obtained their know- 

 ledge from such descriptive non-mathematical 

 works as de la Rive's great treatise on electricity 

 and magnetism. When Maxwell was appointed 

 professor of experimental physics at Cambridge in 

 1871, and the Cavendish Laboratory was opened 

 for work about 1873, quantitative researches at 

 once commenced with Hicks, Gordon, Chrystal, 

 Fleming, Schuster, Glazebrook, and Shaw as 

 early workers. After Maxwell's lamented death 

 in 1879, the late Lord Rayleigh accepted 

 NO. 2610, VOL. 104] 



the position as his successor and directed his 

 attention and great abilities at once to the exact 

 determination of practical electric units, in which 

 he did magnificent service, a work very ably con- 

 tinued by Glazebrook, J. J. Thomson, Searle, and 

 others. After the introduction of public electric 

 lighting, the measurement of electric quantities 

 became a commercial matter. In 1885 the writer 

 of this article read a paper to the Institution of 

 Electrical Engineers in London advocating " the' 

 necessity for a standardising laboratory for elec- 

 trical testing instruments." Soon after, the Board 

 of Trade established such a laboratory, later 

 on the Germans started their " Reichsanstalt," and 

 at a still later stage the National Physical Labora- 

 tory in England was organised and equipped. 



The Cambridge physicists have always main- 

 tained the high standard of research which 

 marked that of Kelvin, Maxwell, and Rayleigh, 

 and much valuable quantitative electrical work 

 has been done there, too extensive for detailed 

 reference. When Sir J. J. Thomson succeeded 

 Lord Rayleigh at the Cavendish Laboratorv he 

 began the epoch-making researches on the nature 

 of electricity and matter which have revolutionised 

 .scientific concepts. His identification of the 

 cathode-ray particle with the electron of Larmor 

 and Johnstone Stoney, and his measurement of its 

 charge and mass, are amongst the most brilliant 

 achievements of experimental science, and opened 

 up an entirely new era in electrical research. J. J. 

 Thomson gathered round him a band of experi- 

 mental investigators whose researches, coupled 

 with his own, threw light on innumerable obscure 

 phenomena. The discovery of X-rays by Rontgen 

 in 1895 and of the Becquerel rays, and the dis- 

 covery of radium by Mme. and Prof. Curie, 

 stimulated the work' of Rutherford, C. T. R. 

 Wilson, Townsend, and others, which has re- 

 sulted in immense accessions to our knowledge 

 : of the nature of electricity and atoms. 



Side by side with this progress in pure scientific 

 knowledge fruitful advances were made in electro- 

 technics. Faraday's great discovery of magneto- 

 electric induction had been long before applied in 

 the construction of machines with permanent 

 magnets for generating, by rotation of coils of 

 wire, an electric current. Henry Wilde had sug- 

 gested the use of electromagnets for producing 

 the magnetic field, and he, as well as Werner, 

 Siemens, and Wheatstone, had discovered the 

 self-exciting principle and applied it in machines. 



