1889.] Prof. C. Lodge on the Discharge of a Leyden Jar.. 413 



WEEKLY EVENING MEETING, 



Friday, March 8, 1889, 



Sir James Crichton Browne, M.D. LL.D. F.R.S. 

 Vice-President, in the Chair. 



Professor Oliver Lodge, LL.D. F.R.S. 



The Discharge of a Leyden Jar. 



It is one of the great generalisations established by Faraday, that all 

 electrical charge and discharge is essentially the charge and discharge 

 of a Leyden jar. It is impossible to charge one body alone. When- 

 ever a body is charged positively, some other body is ipso facto 

 charged negatively, and the two equal opposite charges are connected 

 by lines of induction. The charges are, in fact, simply the ends of 

 these lines, and it is as impossible to have one charge without its 

 correlative as it is to have one end of a piece of string without there 

 being somewhere, hidden it may be, split up into strands it may be, 

 but somewhere existent, the other end of that string. 



This I suppose familiar fact that ail charge is virtually that of a 

 Leyden jar being premised, our subject for this evening is at once 

 seen to be a very wide one, ranging in fact over the whole domain of 

 electricity. For the charge of a Leyden jar includes virtually the 

 domain of electrostatics ; while the discharge of a jar, since it con- 

 stitutes a current, covers the ground of current electricity all except 

 that portion which deals with phenomena peculiar to steady currents. 

 And since a current of electricity necessarily magnetises the space 

 around it, whether it flow in a straight or in a curved path, whether 

 it flow through wire or burst through air, the territory of magnetism 

 is likewise invaded ; and inasmuch as a Leyden jar discharge is 

 oscillatory, and we now know the vibratory motion called light to be 

 really an oscillating electric current, the domain of optics is seriously 

 encroached upon. 



But though the subject I have chosen would permit this wide 

 range, and though it is highly desirable to keep before our minds the 

 wide-reaching import of the most simple-seeming fact in connection 

 with such a subject, yet to-night I do not intend to avail myself of any 

 such latitude, but to keep as closely and distinctly as jDossible to the 

 Leyden jar in its homely and well-known form, as constructed out of 

 a glass bottle, two sheets of tinfoil, and some stickphast. 



The act of charging such a jar I have permitted myself now for 

 some time to illustrate by the mechanical analogy of an inextensiblo 

 endless cord able to circulate over pulleys, and threading in some 

 portion of its length a row of tightly-gripping beads which are con- 

 nected to fixed beams by elastic threads. 



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