628 BELL SYSTEM TECHNICAL JOURNAL 



of frozen helium, at a certain point the resistance suddenh' vanished. 

 I,iterally it x'anished; the word is justified, for the value to which it 

 had dropped was, if not truly zero, at all events not so much as one 

 t"i\e-hiilionth of its value at room-temperature, and not so much as 

 one ten-millionth of its value just before, at about 4.1° K., it suddenly 

 (lisapi)eared. The mercury had altogether lost what had always 

 seemed to be as inseparable a ciualil\' of matter as its inertia or its 

 weight. 



.\ few other elements were later found to share this i>roperty; 

 tin, of which the resistance \anishes at 3.78°; lead, having its thres- 

 hold-temperature at 7.2°; thallium, at 2.3°. Three of these four are 

 C()nsecuti\'e in the procession of elements. Other elements were 

 definitely found not to become "supra-conductive" within the ac- 

 cessible range: gold, cadmium, platinum, copper and iron. In the 

 vicinity of the absolute zero each of these metals has a constant 

 resistance independent of temperature. This as I mentioned was 

 interpreted to mean that these metals, or at least these samples, 

 behaved thus because they were impure — that impurities prevented 

 the vanishing of resistance — but since mercury contaminated in- 

 tentionally with gold or with cadmium was found to become supra- 

 conductive, and tin amalgam likewise, it has become necessary' to 

 save this interpretation, if at all, by assuming that in the five specified 

 metals the impurities coalesce with the metal in some particular way. 

 It is interesting to note that the threshold-temperature of tin amalgam 

 lies abo\-e that of either of its components — at 4.29° K., to be com- 

 pared with the 4.1° of mercury and the 3.78° of tin. These thres- 

 holds are not entirely independent of circumstances; they diminish 

 when a large currenl-densit\- is used, and also when a magnetic field 

 is applied, possibly from the same reason in both cases. 



A number of fantastic things could happen in a world from which 

 electrical resistance had vanished, and one of ilieni was actually 

 realized by Kamerlingh Onnes within tiu' (■(ini|>.iss of his helium- 

 cooled chamber, when a current of tiircc himdrid and l\vcnt\- amperes 

 flowed for half-an-hour ardinui and .irnuiui a iradtn ritii^ with no 

 applied ii.M.i". whatever to inaintaia il, ami did nol lose as much as 

 one (jne-lumdredth of its initial strenglli. In .innllur exix-riment 

 a current of forty-nine ami)eres fiowed for an hour .uound a coil of 

 lead wire of a thousand turns, wound upon a brass tube, and did not 

 lose quite one per cent, of the intensity with which il had been started 

 by removing a magnet of which the field had interlaced the coil. 

 .■\t this rate it would have taken f)ver four da>'s for the current to 

 drop to the 1/cth part of its initial \alue, if the coil could lia\o been 



