XXXIV INTRODUCTION. 



" As a unit of electromotive force, the international volt, which is the electro- 

 motive force that, steadily applied to a conductor whose resistance is one interna- 

 tional ohm, will produce a current of one international ampere, and which is rep- 

 resented sufficiently well for practical use by \%%% of the electromotive force 

 between the poles or electrodes of the voltaic cell known as Clark's cell, at a tem- 

 perature of 15° C, and prepared in the manner described in the accompanying 

 specification.* 



" As a unit of quantity, the international coulomb, which is the quantity of elec- 

 tricity transferred by a current of one international ampere in one second. 



"As a unit of capacity, the international farad, which is the capacity of a con- 

 denser charged to a potential of one international volt by one international cou- 

 lomb of electricity.t 



" As a unit of work, the joule, which is equal to 10^ units of work in the c. g. s. 

 system, and which is represented sufficiently well for practical use by the energy 

 expended in one second by an international ampere in an international ohm, 



"As a unit of power, the watt, which is equal to 10'' units of power in the c. g. s. 

 system, and which is represented sufficiently well for practical use by the work 

 done at the rate of one joule per second. 



" As the unit of induction, the henry, which is the induction in a circuit when 

 the electromotive force induced in this circuit is one international volt, while the 

 inducing current varies at the rate of one ampbre per second. 



" The Chamber also voted that it was not wise to adopt or recommend a stand- 

 ard of light at the present time." 



By an Act of Congress approved July 12th, 1894, the units recommended by 

 the Chicago Congress were adopted in this country with only some unimportant 

 verbal changes in the definitions. 



By an Order in Council of date August 23d, 1894, the British Board of Trade 

 adopted the ohm, the ampere, and the volt, substantially as recommended by 

 the Chicago Congress. The other units were not legalized in Great Britain. 

 They are, however, in general use in that country and all over the world. 



" The kathode on which the silver is to be deposited should take the form of a platinum bowl 

 not less than 10 centimetres in diameter and from 4 to 5 centimetres in depth. 



" The anode should be a plate of pure silver some 30 square centimetres in area and 2 or 3 

 millimetres in thickness. 



" This is supported horizontally in the liquid near the top of the solution by a platinum wire 

 passed through holes in the plate at opposite corners. To prevent the disintegrated silver which 

 is formed on the anode from falling on to the kathode, the anode should be wrapped round with 

 pure filter paper, secured at the back with sealing wax. 



"The liquid should consist of a neutral solution of pure silver nitrate, containing about 15 parts 

 by weight of the nitrate to 85 parts of water. 



" The resistance of the voltameter changes somewhat as the current passes. To prevent these 

 changes having too great an effect on the current, some resistance besides that of the voltameter 

 should be inserted in the circuit. The total metallic resistance of the circuit should not be less 

 than 10 ohms." 



* A committee, consisting of Messrs. Helmholtz, Ayrton, and Carhart, was appointed to pre- 

 pare specifications for the Clark's cell, but no report was made, on account of Helmholtz's death. 



t The one millionth part of the farad is more commonly used in practical measurements, and is 

 called the microfarad. 



