120 THE FIELD OP EXPERIMENTAL RESEARCH. 



It is but a few months since Professor Dewar, by the evaporation of 

 liquid hydrogen in a vacuum, closeh' approached, if he has not reached, 

 our lower limit of possible temperature. Investigations of the effects 

 of low temperature upon the properties of bodies must, from the 

 present outlook, be forever limited to about 20° C. above absolute 

 zero, unless a lighter gas than h}- drogen be discovered upon the earth, 

 the actual existence of which it is, of course, impossible to conjecture. 

 Before the actual experimental demonstration of this limit the limit 

 itself was known to theory, at least approximately, but the spur of the 

 experimenter is the overcoming of difficulties and the possibility of 

 new discoveries which come as surprises. In the case in question a 

 liquid of extremely low density, only one-fourteenth that of liquid 

 nitrogen was produced, while still defined by clear and well-marked 

 refracting surfaces, 



A\'hen we turn to the consideration of the field for research work at 

 high temperatures we are not confronted by the fact of a physical limit 

 existing Avhich may be approached but never reached. We can imag- 

 ine no limit to possible increase of temperature, such as is the absolute 

 zero a limit of decrease. While we may actually employ in electric 

 furnaces temperatures Avhich, according to IVIoissan, have a lower limit 

 of 3,50(1^ C, we can realize the possibility of temperatures existing in 

 the stars measured by tens of thousands or hundreds of thousands of 

 degrees of our temperature scale. 



The moderate increase of working temperature given by the electric 

 furnace enabled Mcissan and others to reap a rich harvest of experi- 

 mental results, and the natural inference is that much more might be 

 expected from further extensions of the limits. These limits are, how- 

 ever, already set for us by the vaporization of all known substances. 

 Our furnace itself keeps down the temperature by melting and vola- 

 tilizing. We may indefinitely increase the energy in an electric arc 

 and thus add to the heat evolved, but the addition only goes to vapor- 

 ize more material. The limit of work then seems to be readily reached 

 in the electric furnace, no materials for lining being available, not 

 subject either to fusion or vaporization, thus using up the energy 

 which would otherwise go to increase the temperature. 



A suggestion as to a possible extension of temperature range may 

 be made here. It may be requisite to work with closed receptacles 

 under pressure, and to discharge through them electric currents of so 

 great energy-value as to attain almost instantaneously the highest 

 temperatures, to be maintained for onl}" a very short time. We may 

 imagine a huge condenser charged to a potential of, sa}^, 10,000 volts 

 as discharged through a limited body of gas contained in a small space 

 within a strong steel tube which has a lining of refractory noncon- 

 ductor. The energy ma}" thus possibly be delivered so suddenly to a 

 verj^ limited body of material as to result in a momentar}^ elevation of 



