[ 358 ] 



LIX. Notes on certain Vibrations produced by Electricity. By 

 J. D. Forbes, Professor of Natural Philosophy in the Univer- 

 sity of Edinburgh^. 



IN the course of last summer (1858), I became acquainted 

 with a phsenomenon described by Mr. Gore in the Philoso- 

 phical Magazine for June (Supplement, p, 519), of the following 

 nature : — A metal cylinder, supported on two metallic rods or 

 rails, the latter being in connexion respectively with the poles of 

 a battery, revolves in either direction, at will, under the action 

 of an electric current copious in quantity. Also continuous rota- 

 tion of a light copper ball, supported on two circular metallic 

 rails, takes place in either direction at pleasure, depending on 

 the first impulse. It appeared to me very probable that this in- 

 teresting fact might be applied to explain what is still obscure 

 in the experiment on heated metals, generally known as the 

 "Trevelyan Experiment,'' described by Mr. Trevelyan in the 

 Edinburgh Transactions, vol. xii., where there is also a paper by 

 myself on the same subject. With a view to elucidate the expe- 

 riment, I had Mr. Gore's circular railway and ball constructed 

 some months since by Mr. Kemp. I had not an opportunity of 

 seeing it tried until October 19, when I found it to answer well 

 with four Bunsen's pairs connected for quantity. The same 

 day, in Mr. Kemp's laboratory, I laid a brass "Trevelyan" bar 

 or rocker on the edge of the brass plate forming the outer rail 

 of Mr. Gore's machine, and connecting the rail with one pole of 

 the same battery, and the bar (by means of a globule of mercury 

 - inserted in a cavity in its upper surface) with the other, energetic 

 vibrations commenced quite resembling those occasioned by heat 

 in the ordinary form of the experiment on a leaden support. 



I have since found, among other results, — (1) That the vibra- 

 tion goes on in whichever direction the electric current passes. 

 [At first I thought that there was a superior elSFect when the cur- 

 rent passed from a good to an imperfect conductor ; but this has 

 not been confirmed, as far at least as I have gone.] (2) The vibra- 

 tions take place both between metals of the same kind and hete- 

 rogeneous metals. (3) When heat is applied to a brass bar 

 vibrating on cold lead, and then electricity is applied as before, 

 the efi'ects are superadded to one another, whichever way the 

 current passes, the vibrations becoming more energetic ; and if 

 there be a musical note, it becomes graver [owing, it is assumed, 

 to the increased arc of vibration] . (4) When a bar of brass was 

 placed so as to vibrate on two parallel upright plates, also of 

 brass, respectively connected with the poles of a battery, the 



* From the Edinburgh New Philosophical Journal for April 1869. 



