A WEEKLY ILLUSTRATED JOURNAL OF SCIENCE. 



Oj Nature trust 



" To the solid ground 

 llic mind which builds for aye. 



-Words worn ii. 



THURSDAY, MARCH 6, 191; 



SCIENTIFIC WORTHIES. 

 XL.— Sir J. J. Thomson, O.M., F.R.S. 



I is iniDossible to think of the rapid and pro- 

 found evolution which occurred in the 

 fundamental conceptions of natural philosophy 

 during the final years of the past century without 

 one figure looming large in the mental picture — 

 that of the celebrated physicist of the University 

 of Cambridge. In effect, the new and fruitful 

 trend assumed by the science of physics in recent 

 years has been in great part due to the happy 

 intuition of Sir J. J. Thomson and to the experi- 

 mental researches unwearyingly pursued by him 

 and his students in the celebrated Cavendish 

 Laboratory. 



One circumstance is particularly striking in that 

 movement — the unforeseen opening out of new 

 .ind vast horizons to the physicist precisely at the 

 moment when the electromagnetic theory of light 

 had been victoriously acclaimed — a theory which 

 not only gathered into one marvellously harmoni- 

 ous synthesis all the phenomena of the physical 

 world, but at the same time satisfied that natural 

 scientific instinct, which seeks for the greatest 

 simplicity in its explanation of natural phenomena, 

 by attributing to a single medium, the sether, the 

 double office of transmitting electrical and mag- 

 netic forces as well as the waves of light. 



In spite of this, physicists were not able long to 

 rest upon their laurels; for certain classes of 

 phenomena, which, perhaps, it was hoped would 

 find an easy explanation, proved quite resistant to 

 elucidation unless accessory hypotheses were 

 devised. 



If we go back in thought fifteen or twenty 

 NO. 2262. VOL. Oil 



years, it is plainly visible that, after the definitive 

 triumph of Maxwell's theory in the experimental 

 field with the work of Hertz and his successors, 

 the great unknown which we call electricity was 

 still considered by all, in its real nature, more or 

 less as an incompressible fluid which could dis- 

 place itself in dielectrics, overcoming a certain 

 elasticity, or flow in a conductor; whilst the 

 principal electrostatic facts, metallic conduction and 

 some other phenomena could be considered as 

 intimately known. But the propagation of 

 electricity in electrolytes, and more especially in 

 gases, remained in part problematical. 



To these two classes of phenomena was not 

 attributed the importance they should have 

 merited. But even then was perceived one most 

 important specific character of electricity in the 

 case of its propagation in electrolytes, namely, its 

 apportionment into small parts, identical among 

 themselves, and representing the charges corre- 

 sponding with each valence of the electrolytic ions. 

 The significance of this fact could not escape the 

 mind of Maxwell ; and it led him to consider those 

 charges as atoms of electricity. Nor could it 

 escape Helmholtz, who acutely pointed out that 

 the existence of such charges must be considered 

 possible, even apart from the ponderable matter 

 with which they are ordinarily accompanied, even 

 if it were only during the short time in which, 

 having left the ion, they are about to enter the 

 electrode to feed the current in the metallic portion 

 of the circuit. 



The existence of atoms of electricity, or of 

 "electrons," according to the felicitous expression 

 proposed by Stoney, was accepted without hesita- 

 tion as a fundamental hypothesis in the theories 

 constructed by Larmor, Lorentz and other mathe- 

 matical physicists; and the former of these so 



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