to the Passage of an Electric Current. 



405 





Sp. gr. (density 

 of water at 18° C. 

 taken as 1). 



Section in square 



inches, deter- 

 mined from loss 

 of weight in 

 water at 4° O. 



Increase of re- 

 sistance of 1 cub. 



centim. for a 

 stretching-force 

 of 1 gramme, 

 =k. 



Eesistance of 1 

 cub. centim. of 

 the wire, 

 =s. 



Steel. 



No. 1 



» 2 



„ 3 



„ 4 .... 



„ 5 (Commercial 1 

 steel) .... J 



7-8630 

 7-8240 

 7*794o 

 7-8280 



7-7072 



2231 x 10-7 

 6528 X 10-7 

 lzooo X 10 ' 

 21009x10-7 



8477x10-7 



Ohms. 

 3009xl0-!7 

 3159x10-17 

 3445 x 10-17 

 2982x10-17 



3511x10-17 



Ohms. 

 1574-8x10-8 

 1653-1x10-8 

 1882*4 x 10 s 

 1628-7x10-8 



1847-0x10-8 



Iron. 



No. 1 



„ 2 



„ 3 



7-7496 

 7-5300 

 7-6409 



5003x10-7 

 10239x10-7 

 19010x10-7 



2557x10-17 

 2637x10-17 

 2712x10-17 



1217-6x10-8 

 1200-8xl0- 8 

 1291-0x10-8 



Brass. 



„ 2 



„ 3 



„ 4 



8-4984 

 8-4965 

 8-5048 



O / ol X 1U ' 

 8782x10-7 

 11327x10-7 

 18258x10-7 



1729x10-17 

 1565x10-17 

 1809x10-17 



CKKCK.*7 vlA-8 

 DOD / X lv ° 



782-2x10-8 

 744-8x10-8 

 742-9x10-8 



The values of h, divided by those of s, will give the increase of resist- 

 ance for a stretching-weight of 1 gramme per unit of resistance. The 



following Table gives the values of — for the different wires : — 



Values of — , or increase of resistance per unit of resistance for a stretch- 

 s 



ing-weight of 1 gramme on a cubic centim. of the material. 

 Steel. 



(1) 1910-4x10-12^ 



(2) 1910-4xl0-i 2 | Mean = 1875-5x 10-i 2 . Greatest de- 



(3) 1830-5 x 10 _12 y parture from mean value less than 



(4) 1825-5 x IO-12 | 2-7 per cent. 



(5) 1900-7 x IO-12 J 



Iron. 



S :::::::: Sxlo^l^r 21 , 32 -^ 10 - 12 - 



^ 2100'1 X 10~ 12 J P arture * rom m ean about 3 per cent. 



