VIIT. MEASUREMENT. 283 



than their bases. Increase in the current passing by means of the wires be- 

 tween the electrodes causes the liquid to rise higher in the manometer tube, 

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



1404. The Voltaic Compensator, an apparatus for main- 

 taining constant the intensity of the electric current derived from 

 nny sort of voltaic battery. 



Elie Wartmann, Professor of Natural Philosophy in the 

 University of Geneva. 



The voltaic compensator is an apparatus which keeps the intensity of the 

 current from any voltaic battery constant. A full description is printed in 

 the number for January 1858 of the "Archives des Sciences physiques et 

 naturelles." In addition to the principal current, which, if constant, would 

 do the work required, there is an auxiliary one, the strength of which is 

 kept down by inserting an additional resistance. This resistance diminishes 

 with the weakening of the principal current, and the consequent increase of 

 the auxiliary current compensates that weakening. 



14O4a. Regulator, by Foucault. M. J. Duboscq, Paris. 



1405. Apparatus to make the Electric Light, derived 

 from a Voltaic Battery, constant in its position and intensity. 



Elie PPartmann, Professor of Natural Philosophy in the 

 University of Geneva. 



An apparatus called a fixator of electric light, used in the years 1856 and 

 1857 for lighting the harbour of Geneva. A full description is to be found 

 in the number for December 1857 of the "Archives des Sciences physiques 

 et naturelles." By means of an electro-magnet and of gravity, two points 

 of carbon are placed and kept at such a distance that the light produced by 

 the current of an electric battery may be as bright as possible. 



1406. Regulator of Electric Currents, after the plan of 

 M. Mascart. M. Redier. 



1407. Regulator for the Electric Light. M. Carre. 



1408. Artificial Charcoal Sticks for the Electric Light. 



M. Carre. 



1409. Electric Lamps. These lamps are automatic in their 

 action, in them the carbon points are caused to approach or recede 

 from each other as required, without the aid of clockwork. 



Siemens and Halske, Berlin. 



VIII. APPARATUS FOR DETECTING AND MEASUR- 

 ING DIFFERENCES OF ELECTRIC POTENTIAL 

 AND CURRENTS OF ELECTRICITY. 



a. ELECTROSCOPES AND ELECTROMETERS. 



1410. Two Repulsion Electrometers constructed and 

 used by Van Marum. Teyler Foundation^ Haarlem. 



