268 GREAT MEN OF SCIENCE 



From the units of current and voltage thus settled, Weber 

 was able, by means of Ohm's law, at once to deduce the abso- 

 lute unit of resistance (to-day called the ohm), which is par- 

 ticularly suited for realisation and preservation in the form of 

 wire, or much better still, in the form of a thread of mercury, 

 as used by Siemens since i860 (Siemens unit); and hence a 

 large number of Weber's latest measurements related to this 

 unit. Since the means required for this purpose con- 

 tinually increased, but the State believed it necessary to 

 economise, Weber made use, for the first time, of the money 

 subscribed for him when he was dismissed from office. 

 Weber was not able to witness the complete realisation of all 

 the refinements which he had planned for settling the elec- 

 trical units, in spite of the high age of eighty-six which he 

 reached; but what he began was continually pursued, most 

 of all in Germany, and resulted in our present-day certainty 

 in electrical measurement, which fulfils every possible re- 

 quirement. 



During Weber's lifetime, in the year 1881, there was a 

 Congress in Paris, which arranged the international accep- 

 tance of the system of units founded by Gauss and Weber. 

 Here the main question was the settlement of factors by 

 which the absolute units were to be multiplied in order to 

 provide practical units of a suitable size, and also to fix short 

 names for the units. The numerical factors were neces- 

 sary, since all the units had been derived from the three fun- 

 damental units of space, mass and time, solely by means of 

 natural laws and without any reference to their size. Thus 

 for example, the absolute unit of electromotive force would 

 have been much too small for ordinary use, and it was de- 

 cided to use a unit 100,000,000 times as large, and call it the 

 'volt.' For all this, and also for the settlement of the funda- 

 mental units (whether, for example, the centimetre or the 

 millimetre was to be taken as unit of length) an agreement 

 between the various countries was necessary, and such an 



