624 BELL SYSTEM TECHNICAL JOURNAL 



the last element of the series; but the conductivity of silver stands 

 to the conductivity of sulphur in the ratio 10^'. The distance from 

 the sun to the nearest star is some 10'* cm.; we see that a sheet of 

 sulphur a thousandth of an inch thick would offer more of an obstacle 

 to the passage of electricity than a cable of silver of the same diameter, 

 extending from the earth to Alpha Centauri. The variations of 

 conducting-power from element to element arc thus as fantastically 

 great as the variations in scale from the world of common life to the 

 world of interstellar spaces. The conductivities of the metals, how- 

 ever, are confined within a narrow fraction of this range; it is between 

 the metals and the non-metals, and between one non-metallic element 

 and another, that the leaps are surprisingly great. 



In general, too, the resistance of a non-metallic element decreases 

 as its temperature is raised; the curve of resistance versus tempera- 

 ture (I shall often call it characteristic, henceforward) slants down- 

 ward, the derivative and the temperature-coefficient of resistance 

 are negative. Near room-temperature this is the usual behavior, 

 but not always over the entire accessible range; of some elements it 

 is observed that the resistance declines less rapidly as the temperature 

 is raised, the curve is concave upward; eventually the decline ceases, 

 the resistance passes through a minimum value at a certain char- 

 acteristic temperature, and thereafter increases with the temperature 

 as the resistances of metals do. At least one element of the debatable 

 class (germanium) exhibits a characteristic curve that slants upward 

 instead of downward at room-temperatures; but when the curve is 

 followed towards lower temperatures, it too is found to be concave 

 upward with a minimum of resistance below— 100° C. This suggests 

 that for all of the non-metals the resistance-temperature curve may 

 be a loop bulging downward, with a minimum at a certain temperature 

 that varies from element to element: on this generalization f)ne of 

 the contemporary theories is founded. 



These rules can be illustrated by mentidning briefly the heh.ixior 

 of the non-metallic elements one by one. Beginning at the fnni 

 of the procession of elements, we pass over hydrogen (no data), lithiuin 

 and beryllium (metals), and commence with boron. Boron has a \ery 

 high resistance at room temperature, which drops a hundredfold 

 when it is heated to 180° C. and ten-million-fold when it is raised to 

 a red heat. On carbon a tremendous amount of work has been done, 

 which unfortunately largely goes to show that the word "carbon" 

 usually signifies a framework of carbon atoms packed with occluded 

 gases, organic compounds, and impurities of divers kinds, which no 

 known mode of treatment avails to expel entirely, although almost 



