228 HISTORY OF COLD AND THE ABSOLUTE ZERO. 



be collected in a vacuum vessel the outer walls of which are iuiinersed 

 in liquid hydrogen. The practical difficulties and the cost of the oper- 

 ation will be ver}^ great; but on the other hand, the descent to a tem- 

 perature within 5' of the zero would open out new vistas of scientific 

 inquir}^ which would add immensely to our knowledge of the proper- 

 ties of matter. To command in our laboratories a temperature which 

 would be equivalent to that which a comet might reacli at an infinite 

 distance from the sun would indeed be a great triumph for science. 

 If the present Roj^al Institution attack on helium should fail, then we 

 must ultimately succeed b}' adopting a process based on the mechan- 

 ical production of cold through the performance of external work. 

 When a turbine can be worked by compressed helium, the whole of the 

 mechanism and circuits being kept surrounded with liijuid hydrogen, 

 then we need hardly doubt that the liquefaction will ])e efl'ected. In 

 all probability gases other than helium will ))e discovered of greater 

 volatility than h^^drogen. It was at the British Association meeting, 

 in 1896, that I made the first suggestion of the probalile existence of 

 an unknown element which would be found to fill up the gap between 

 argon and helium, and this anticipation was soon taken up by others 

 and ultimately confirmed. Later, in the Bakerian Lecture for 1901, 

 I was led to infer that another mem))er of the helium group might 

 exist having the atomic weight a])out 2, and this would give us a gas 

 still more volatile with which the absolute zero might be still more 

 nearly approached. It is to l)e hoped that some such element or ele- 

 ments may yet be isolated and identified as coronium or nebulium. If 

 among the unknown gases possessing a very low critical point some 

 have a high critical pressure instead of a low one, which (uxlinary 

 experience would lead us to anticipate, then such diflicultly li([uefiable 

 gases would produce fluids having difi'erent physical properties from 

 any of those with which we are acquainted. Again, gases ma}^ exist 

 having smaller atomic weights and densities than hydrogen, yet all 

 such gases nnist, according to our present a lews of the gaseous state, 

 be capable of liquefaction before the zero of temperature is reached. 

 The chemists of the future will find ample scope for investigation 

 within the apparently limited range of temperature which separates 

 solid hydrogen from the zero. Indeed, great as is the sentimental 

 interest attached to the licpiefaction of these refractory gases, the 

 importance of the achievement lies rather in the fact that it opens out 

 new fields of research and enormously widens the horizon of physical 

 science, enabling the natural philosopher to study the properties and 

 behavior of matter under entirely novel conditions. This department 

 of inquiry is as yet only in its infancy, but speedy and extensive devel- 

 opments may be looked for, since within recent vears several special 

 cr3^ogenic laboratories have been established for the prosecution of 

 such researches, and a licjuid-air plant is becoming a common adjunct 

 to the equipment of the ordinar}^ lal)oratory. 



