IX. - RESISTANCE. 297 



1499a. Compensator, by Froinent. 



Polytechnic School, Pat-is. 



1500. Post Office Resistance Coil, as used by the Govern- 

 ment telegraph authorities, for testing the resistance of telegraph 

 lines, cables, batteries &c. Elliott Brothers. 



These coils are constructed on the Wheatstone's bridge principle, and the 

 arrangement allows of the measurement of resistances from T i^ to 1,000,000 

 Ohms. 



1501. Dial Resistance Coil, for testing the resistance of 

 telegraph lines, cables, batteries, &c. Elliott Brothers. 



These coils are capable of greater accuracy than other resistance coils. 

 For each dial only one plug is used to bring the desired resistance in circuit, 

 or every change, therefore, the same number of plugs is necessary. 



1502. Preece's Balance, for comparing resistances in con- 

 nexion with a set of resistance coils. Elliott Brothers. 



This instrument is on the principle of the Wheatstone's bridge, and contains 

 four pairs of equal resistances, a commutator, and two keys. 



1503. Set of Resistance Coils, German silver, with Wheat- 

 stone's bridge, for testing the resistance of telegraph lines, cables, 

 batteries, &c. These coils allow of measurements of resistance 

 from ^ to 1,000,000 Ohms. Elliott Brothers. 



1504. British Association Unit or Ohm, of German silver 

 wire, equal to 10 absolute electro-magnetic units, the standard of 

 electrical resistance. Elliott Brothers. 



15O4a. Large Set of Resistance Coils, with Bridge (a 



new form and arrangement). Warden, Muirhead, and Clark. 



15O4b. New combined Set of Thomson and Varley's 

 Resistance Slides (a new form and arrangement). 



Warden. Muirhead, and Clark. 



1504c. Set of Resistance Coils (small portable set), con- 

 taining 10,000 B A units in the aggregate, and set of propor- 

 tional coils for same. Warden, Muirhead, and Clark. 



15O4d. Condenser, 20 microfarads. 



Warden, Muirhcad, and Clark. 



1504:6. Small portable Standard Condenser, capacity 

 1 microfarad in aggregate, divided in : 1 : 2 : 3 : 4 microfarads. 



Warden, Muirhead, and Clark. 



15O4rf. Standard Condenser, microfarad. 



Warden, Muirhead, and Clark. 



