s<».W/; CUXTF.Ml'OR.'IRY .IDy.lNCliS IW I'liysiCS f (,27 



Ixil iiol always, the extra roctlirient h is positive; the characteristic 

 is concave upward. "I'sually l)iit not alwa\'s" is a phrase much 

 in (lenuind when one is layin>j down rules for conducting bodies. 

 In this case metals of the platinum triad furnish the exceptions. 

 In other instances (•id)ic terms must be added to the formula-, and 

 in still others e\en these are inade(|uate. One of the longest charac- 

 teristics e\er traced, the one determined by Worthing and Korsythe 

 lor timgsten from 14(M)° to 3250° C, conforms to the equation 

 R --const. 7'-. 



.-\1I these details .ibont \ .dues of resistances and shapes of resistance- 

 temfierature cnr\es are sedate and commonplace enoujjh; but there 

 is one quite extraordinary phenomenon in this field, one of the strange 

 discontinuities which appear here and there in the theatre of nature 

 .md contribute more of dramatic interest to the spectacle than any 

 amount of smooth correlations between continuous variables. Kx- 

 tensions of the characteristics downwards toward the absolute zero 

 have to follow upon improvements in the art of producing and main- 

 taining ver>- low temperatures; and for the last twenty years the 

 advances in this art have been made in the Cryogenic Laboratory 

 of the I'niversity of Leyden, and there the curves have been extended 

 downwards step by step as additional ranges of cold were made 

 accessible. The temperatures down to 14° K. attained with liquefied 

 hydrogen did not alTect the resistances of metals in any very startling 

 way. although the characteristics are generally more sharply cur\ed 

 there than at or(linar%' temperatures; but w-hen with the aid of liquefied 

 helium Kamerlingh Onnes penetrated to within five degrees of the 

 ■d)solute zero, something astonishing took place. 



Kamerlingh Onnes had been experimenting with platinum wire, 

 and he had found that over the interval of temperatures newly made 

 available, the interval from 4.3° to 1..5° K. (a small range when meas- 

 ured in degrees, but a great one when considered in terms of the dis- 

 tance between its lower limit and the absolute zero) the resistance of 

 the wire did not change. Thishe thought might mean that the proper 

 resistance of the metal had become exceedingly small, leaving as 

 the chief comixment of the observed resistance a term imaffected by 

 temperature and due possibly to .some such thing as discontinuities in 

 the wire, for example between the platinum and bits of impurities 

 mixed into it. To have a purer metal he replaced the platinum by 

 rejieatedly-distilled mercury. It was contained in a slender gla.ss 

 capillarv' tulie, forming so fine a filament that the resistance at room- 

 temperature was rather considerable; in one specified instance, 173 

 ohms. When he lowered this filament of mercury to the temperature 



