SCIENTIFIC AND TECHNICAL LABOURS TO 1860. 237 



electrolysis. They are put by it into the so-called 

 active state, rendering them capable of forming directly 

 with other gases chemical compounds, which could 

 otherwise only be obtained in a very roundabout way. 



I have already mentioned that even in the middle 

 of this century one of the greatest obstacles in the 

 way of the development of the physical sciences, and 

 especially of physical technology, was the want of fixed 

 standards. In scientific writings pretty generally metre 

 and gramme were used as measures of length and 

 weight, but notwithstanding technology suffered from 

 an insupportable looseness and inaccuracy. Metre and 

 gramme at any rate always formed fixed points of 

 comparison, to which all estimates of measure could 

 be referred. Such a fixed point was entirely wanting, 

 however, for electric standards. William Weber indeed 

 had already, in conjunction with Gauss, theoretically 

 developed the admirable system of absolute magnetic 

 and electric units, and had also perfected to an ex- 

 traordinary degree the methods of exact measurement 

 and the requisite instruments, but standard tallies, 

 representing the absolute units and accessible to every- 

 body, were wanting. It was in consequence usual for 

 every physicist to set up his own standard of resistance, 

 which was attended by the serious inconvenience that 

 the results of his labours w r ere not then comparable 

 with those of others. 



Jacobi in St. Petersburg then made the proposal 

 to take as general unit of resistance an arbitrarily 

 chosen copper wire, which he deposited with a Leipzig 



