576 



SCIENCE. 



[N. S. Vol. XVI. No. 406. 



that many changes in the properties of 

 substances have been found to vary stead- 

 ily 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 direc- 

 tion in those which are as yet unexplored. 

 Of such a breakdown low-temperature re- 

 search has already jaelded a direct proof 

 at least in one case. A series of experi- 

 ments with pure metals showed that their 

 electrical resistance gradually decreases as 

 they are cooled to lower and loAver tem- 

 peratures, in such ratio that it appeared 

 probable that at the zero of absolute tem- 

 perature they would have 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 re- 

 frigerants. But with the advent of the 

 more powerful refrigerant liquid hydrogen 

 it became necessary to re\ase 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 knowTi liquids, 

 when forced to evaporate quickly by being 

 placed in the exhausted receiver of an air- 

 pump, undergo a reduction in tempera- 

 ture, but when hydrogen was treated in 

 this way it appeared to be an exception. 

 The resistance thermometer showed no 

 such reduction as was expected, and it be- 

 came a question whether it was the hydro- 

 gen or the thermometer that was behaving 

 abnormally. Ultimate^, by the adoption 

 of other thermometrical appliances, the 

 temperature of the hj^drogen was proved 

 to be lowered by exhaustion as theory in- 

 dicated. Hence it was the platinvmi ther- 

 mometer which had broken down ; in other 

 words, the electrical resistance of the metal 



employed in its construction was not, at 

 temperatures about minus 250° C, de- 

 creased by cold in the same proportion as 

 at temperatures about minus 200°. This 

 being the case, there is no longer any rea- 

 son to suppose that at the absohite zero 

 platinum would become a perfect conductor 

 of electricity; and in view of the similar- 

 ity between the beha-\dor of platinum and 

 that of other pure metals in respect of tem- 

 perature and conducti%'ity, the presump- 

 tion is that the same is trae of them also. 

 At any rate, the knowledge that in the case 

 of at least one property of matter we have 

 succeeded in attaining a depth of cold suf- 

 ficient to bring about unexpected change 

 in the law expressing the variation of that 

 property with temperature, is sufficient to 

 show the necessity for extreme caution in 

 extending our inferences regarding the 

 properties of matter near the zero of tem- 

 perature. Lord Kelvin evidently antici- 

 pates the possibility of more remarkable 

 electrical properties being met with in the 

 metals near the zero. A theoretical inves- 

 tigation on the relation of 'electrions' and 

 atoms has led him to suggest a hjT)othetical 

 metal having the following remarkable 

 properties ; below one degree absolute it is 

 a perfect insulator of electricity, at two de- 

 grees it shows noticeable conductivity, and 

 at six degrees it possesses high conductiv- 

 ity. It may safety be predicted that liquid 

 hydrogen will be the means bj^ which many 

 obscure problems of physics and chemistry 

 will ultimately be solved, so that the lique- 

 faction of the last of the old permanent 

 gases is as pregnant now with future con- 

 sequences of great scientific moment as was 

 the liquefaction of chlorine in the early 

 years of the last century. 



The next step towards the absolute zero 

 is to find another gas more volatile than 

 hydrogen, and that we possess in the gas 

 occurring in clevite, identified by Kamsay 

 as helium, a gas which is widely distrib- 



