VII. CURRENTS. 327 



1398a. General Table, by Ampere, with apparatus used by 

 him in the discovery of the action of currents. 



College of France, Paris. 



1399. Apparatus for demonstrating the action of Me- 

 tallic Discs in movement upon a metallic wire used as a voltaic 

 conductor. P r f- Daniel Colladon, Geneva. 



Experiment performed on 4th September 1826, in presence of the Paris 

 Academy of Sciences, by Messrs. Ampere and Coliadon. 



Bulletin de Sciences Mathematiques, by De Ferussac, vol. 6, p. 212. 



1400. Model of a Circular 11 ail way, for showing the 

 rotation of a metal ball upon it by the passage of an electric 

 current. George Gore, F.R.S. 



(See Philosophical Magazine, Feb. 1859.) 



140Oa. Small Model of a Circular Railway, for showing 

 the rotation of a metal ball upon it by the passage of an electric 

 current. (See Philosophical Magazine, February 1859.) 



George Gore, F.R.S. 



VII. APPARATUS FOR REGULATING THE 

 STRENGTH OF ELECTRIC CURRENTS. 



1402. Wheat stone's Rheostat, or changeable resistance, for 

 quickly adding or removing a low resistance. Elliott Brothers. 



1403. Voltastat and Voltameter combined. 



Frederick Guthrie. 



Air-tight through the stopper of a cylindrical vessel containing dilute sul- 

 phuric acid pass the following: (I.) Two platinum wires coated with glass. 

 (2.) A long and wide tube open at both ends, the lower end reaching to the 

 bottom of the cylinder. (3.) A tube opening freely beneath the stopper and 

 above it by a very fine capillary aperture. The platinum wires are enlarged 

 into platinum plates of triangular form, with their apices downwards, and 

 further apart than their bases. Increase in the current passing by means of 

 the wires betAveen the electrodes causes the liquid to rise higher in the mano- 

 meter tube, and also, by laying bare the electrodes, increases the resistance. 



1404. Voltaic Compensator, an apparatus for maintaining 

 the electric current derived from any sort of voltaic battery at 

 constant intensity. 



Elie Wartmann, Professor of Natural Philosophy at the 

 University of Geneva. 



A full description of this instrument is printed in the "Archives des 

 Sciences physiques et naturelles," January 1858. In addition to the principal 

 current, which, if constant, would do the work required) there is an aux- 

 iliary one, the strength of which is kept down by inserting an additional 



