8 ELECTRIC LIGHTING. 



The resistance of metals increases, however, with the tem- 

 perature, while on the other hand that of liquids and gases 

 decreases. The co-efficients of correction which must be 

 applied to the figures we give in the table below in order to 

 obtain the true value for a given temperature, may be seen in 

 my Expose des applications de r electricity tome I ^ pp. 37 ct 



453- 



The conductivity of a body is its property of transmitting an 

 electric current more or less easily. Properly speaking, all 

 the substances of nature are conductors, but in very different 

 degrees and under very different conditions. Metals are the 

 best conductors. Resins, and other substances like India- 

 rubber, gutta-percha, glass, &c., have less conducting power. 

 Liquids and gases are also conductors, but under certain 

 conditions. 



The conductivity of bodies may be considered from seve- 

 ral points of view. When it allows the electricity to pene- 

 trate the whole mass of a body without further actionj and 

 to be propagated within it like heat, it takes the name of 

 conductivity proper. When, on the contrary, it results only 

 from the effects of successive chemical decompositions and 



Resistance in Conducting 



Ohms. Power. 



Annealed Copper 0*02057 ... 



Drawn Copper 0*02104 ... 99'55 



Annealed Gold 0*02650 



Drawn Gold 0*02697 77'9& 



Annealed Aluminium 0*03751 ... . - 



Compressed Zinc 0*07244 ... 29*02 



Annealed Platinum 0*11660 ... * 



,, Iron 0*12510 ... 16*81 



,, Nickel 0*16040 ... 13 *i i 



Compressed Tin 0*17010 ... 12*36 



,, Lead 0*25270 ... 8*32 



Antimony 0*45710 ... 4*62 



,, Bismuth 1*68900 ... 1*24 



Liquid Mercury 1*27000 



Alloy of Platinum and Silver 0*31400 ... 



German Silver 0*26950 ... - 



Alloy of Silver and Gold 0*13990 ... "" 



