410 APPENDIX. 



APPENDIX. 



PROPOSED REVISION OF ELECTRICAL UNITS. 



While the concluding sheets of this little work have been 

 passing through the press an important change in the names of 

 the units used for practical measurement has been suggested by 

 the International Congress of Electricians at Paris. 



The name of ampere is henceforth to be assigned to the unit 

 of current^ which in these Lessons is called "one weber-per- 

 second." 



The name of coulomb is to be given to the unit of quantity r , 

 called in these Lessons "one weber." 



Whether these names will be adopted by practical electricians 

 and telegraphists remains to be seen. In Great Britain it has 

 of late become the fashion to use the term weber for the unit of 

 current, as being shorter than the more accurate "weber-per- 

 second." 



It has also been decided by the International Congress that 

 a fresh evaluation shall be made of the ohm ; and that, when 

 this is completed, standards shall be constructed on the plan 

 originally suggested by Siemens, by defining the practical ohm 

 as the resistance of a column of pure mercury of a certain length 

 and of one millimetre of cross-section. The length will be 

 known exactly only when the new evaluation is completed. 

 It will be between 104*5 an d J O5 centimetres. 



