308 Scientific Intelligence. 



extremely improbable. A thermometer introduced into regions 

 outside the uttermost confines of the earth's atmosphere might 

 approach the absolute zero, provided that its parts were highly- 

 transparent to all kinds of radiation, otherwise it would be 

 affected by the radiation of the sun, and would therefore 

 become heated. But supposing all difficulties to be overcome, 

 and the experimenter to be able to reach within a few degrees of 

 the zero, it is by no means certain that he would find the near 

 approach of the death of matter sometimes pictured. Any fore- 

 cast of the phenomena that would be seen must be based on the 

 assumption that there is continuity between the processes studied 

 at attainable temperatures and those which take place at still 

 lower ones. Is such an assumption justified ? It is true that 

 many changes in the properties of substances have been found to 

 vary steadily with the degree of cold to which they are exposed. 

 But it would be rash to take for granted that the changes which 

 have been traced in explored regions continue to the same extent 

 and in the same direction in those which are as yet unexplored. 

 Of such a breakdown low-temperature research has already yielded 

 a direct proof at least in one case. A series of experiments with 

 pure metals showed that their electrical resistance gradually 

 decreases as they are cooled to lower and lower temperatures, in 

 such ratio that it appeared probable that at the zero of absolute 

 temperature they would ha\e no resistance at all and would 

 become perfect conductors of electricity. This was the inference 

 that seemed justifiable by observations taken at depths of cold 

 which can be obtained by means of liquid air and less powerful 

 refrigerants. But with the advent of the more powerful refrig- 

 erant liquid hydrogen it became necessary to revise that conclu- 

 sion. A discrepancy was first observed when a platinum resistance 

 thermometer was used to ascertain the temperature of that liquid 

 boiling under atmospheric and reduced pressure. All known 

 liquids, when forced to evaporate quickly by being placed in the 

 exhausted receiver of an air-pump, undergo a reduction in tem- 

 perature, but when hydrogen was treated in this way it appeared 

 to be an exception. The resistance thermometer showed no reduc- 

 tion as was expected, and it became a question whether it was 

 the hydrogen or the thermometer that was behaving abnormally. 

 Ultimatel}^, by the adoption of other thermometrical appli- 

 ances, the temperature of the hj^drogen was proved to be lowered 

 by exhaustion as theory indicated. Hence it was the platinum 

 thermometer which had broken down ; in other words, the elec- 

 trical resistance of the metal employed in its construction was 

 not, at temperatures about mi7ius 250° C, decreased by cold in 

 the same proportion as at temperatures about mmus 200°. This 

 being the case, there is no longer any reason to suppose that at 

 the absolute zero platinum would become a perfect conductor of 

 electricity ; and in view of the similarity between the behavior 

 of platinum and that of other pure metals in respect of tempera- 

 ture and conductivity, the presumption is that the same is true of 



