FUNDAMENTAL . UNITS OF MEASURE. 147 



edge and experience among electricians was suck as to indicate that 

 the time was ripe for the general adoption of the principal nnits of 

 electrical measnre. An International Congress of Electricians was 

 arranged for, to meet in Chicago, during the World's Columbian Ex- 

 position of 1<S93. In this Congress the business of dettuiug and naming 

 units of measure was left to what was known as the " Chamber of 

 Delegates," a body composed of those only who had been officially 

 commissioned by their respective governments to act as members of 

 said Chamber. The United States, Great Britain, Germany, and 

 France were eachallowed five delegates in the Chamber. Other nations 

 were represented by three, two, and in some cases one. The princi- 

 pal nations of the world were represented by their leading electricians, 

 and the Chamber embraced many of the most distinguished living 

 representatives of physical science. 



The delegates representing the United States have reported to the 

 honorable the Secretary of State, under date of November 6, .1893, 

 giving the names and definitions of the units of electrical measure as 

 unanimously recommended by the (Uiamber in a resolution as follows: 



^^ Resolved, That the several governments rei)resented by the dele- 

 gates of this International Congress of Electricians be, and they are 

 hereby, recommended to formally adopt as legal units of electrical 

 measure the following: As a unit of resistance, the internatiomtl ohm^ 

 which is based upon the olim equal to 10^ units of resistance of the 

 Centimeter-Gramme-Second system of electro-magnetic nnits, and is 

 represented by the resistance offered to an unvarying electric current 

 by a column of mercury at the temperature of melting ice li-J:.")!}! 

 grammes in mass, of a constant cross-sectional area and of the length 

 of 10(5.3 centimeters. 



"As a unit of current, the International ampere, which is one-tenth of 

 the unit of current of the c. G. s. system of electro-magnetic units, and 

 which is represented sufficiently well for practical use by the unvarying 

 current which, when ])assed through a solution of nitrate of silver in 

 water, and in accodrance with accompanying specifications,* deposits 

 silver at the rate of 0-001118 of a gramme per second. 



* In the following specification tlie term silver voltameter means the arrangement 

 of apparatus by means of wliicli an electric current is passed tlirougli a solution of 

 nitrate of silver in Avater. The silver voltameter measures the total electrical quan- 

 tity which has passed during the time of the experiment, and by noting this time, 

 the time average of the current, or if the current has been kept constant, the cur- 

 rent itself can be deduced. 



In employing the silver voltameter to measure currents of about 1 ampere, the 

 following arrangemc^nt^ should be adopted : 



The kathode on which the silver is to be dejjosited should take the form of a plat- 

 inum bowl, not less than 10 centimeters in diameter and from 4 to 5 centimeters in 

 depth. 



The anode should be a jdate of \n\vv silver some 30 s<iuaro centiiueters in area and 

 2 or 3 millimeters in thickness. 



This is supported horizontally in the li(|uid near the top of the solution by a, plat- 

 inum 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. 



