362 Dr. Matthiesaen on the Specific Resistance of the Metals 



Table I. 



Resistance in terms 

 of B.A. unit (1864). 



Copper 01469 



Silver ...... 0-1689 



Gold 0-4150 



Lead 2-257 



Mercury 13*071 



Gold-silver alloy . . . 1668 



These values are called by Professor William Thomson and 

 Mr. Jenkin the specific resistances of the metals at 0° referred 

 to unit of mass and length. 



When carrying out the above determinations, we did not think 

 of taking the specific gravity of the wires employed, as our object 

 was only to see to what accuracy we could reproduce resistances 

 by using wires of the above metals, &c. We employed the length 

 weight in preference to the length section, knowing that the 

 weight of a wire may be much more accurately determined than 

 its section, whether deduced directly from the measurements of 

 the diameter or indirectly from the specific gravity, the determi- 

 nation of the latter introducing a certain error. Of course, in 

 endeavouring to reproduce resistances, it is wise to avoid the use 

 of any unnecessary values ; and it is just as well, and certainly a 

 much more accurate method, to determine a resistance in length 

 weight than in length section. 



A strict comparison with former values will not be possible, 

 owing to the above fact. Approximately, we may compare them 

 by using the following specific gravities : — 





Table II. 





Resistance in terras 

 of the B. A. unit. 

 Specific gravity. 

 Silver* . . 10-50 002048 



Conducting-power 

 of hard-drawn wires 

 of metre length and 

 millimetre diameter. 

 48-83 



Copper* . 8-95 

 Gold* . . 19-27 



0-02090 

 0-02742 



47-85 

 36-47 



Lead* . . 11-391 



0-2527 



3-957 



Mercury . 13*595 

 Gold-silverf 15-218 



1-224 

 0-1399 



0-8172 

 7-148 



Or taking the conducting-power of the gold-silver alloy, 7*148 

 = 15'03, the following will be the values of the conducting- 

 powers of the metals and some of their alloys : — 



* Of cast specimens. 



t Of the wire. 



