340 THE ELECTRIC TELEGRAPH. 



doing this they have lost sight of the dignified position 

 which they held as an impartial jury at starting in their 

 duties, and have attached themselves exclusively to the 

 cause of the so-called " absolute system/' and issued an 

 unit whose agreement with the defined " absolute unit " is 

 by no means certain a proceeding which has had for its 

 consequence not only that they have shut their eyes to many 

 points of great merit in other systems, but have also attacked 

 them, in certain instances, with so much apparent animus, 

 that, if we did not know better, we might almost suspect 

 some of them of having some little personal feeling in the 

 matter. 



The B. A. unit is, however, in all probability a very near 

 approximation to the value 10 7 ^5 units. It may be as near 

 an approximation to its original as the mercury units which 

 have been determined are to be the defined unit, or as any 

 of the alloys of gold and silver are to be defined alloy. All 

 these are of course only approximations ; but we are certain 

 that with the two last systems these approximations may be 

 brought with certainty infinitely nearer to their true values, 

 because the manipulations and the sources of error are less 

 than those which profess to represent the absolute system ; 

 and therefore these systems are better adapted to supply the 

 unit of resistance. 



In a practical sense, it is of importance to have the unit 

 of resistance that of some geometrical body of the material 

 taken as unit of conducting power. Beyond this we do not 

 see that it matters much what expresses the unit so long as 

 one system only is adopted, which is capable of reproduction 

 if this should become necessary, and correct resistance-scales 

 constructed to it. 



But while the electric permanency of solid metals is still 

 an open question, whatever objections may be tenable against 

 reproductions we must nevertheless return to them, from time 

 to time, to control our resistances. For this purpose, then, 

 the exactest and simplest method of reproduction must be 

 available. Weber's system for this would be scarcely suitable ; 

 first, because it lacks the certainty of the condition of exact- 



