The Nadir of Temperatvjp and Allied Problems. 41.5 



WEEKLY EVENING MEETING, 



Friday, June 5, 1908. 



His Grace The Duke of Northumberland, K.G. P.O. D.C.L. 

 LL.D. F.R.S., President, in the Chair. 



Professor Sir James Dewar, M.A. LL.D. D.Sc. F.R.S. M.R.I.^ 

 Fullerian Professor of Chemistry R.I. 



The Nadir of Temperature and Allied Problems. 



[abstract.] 



Many years ago the zenith of temperature and the intensity of solar 

 heat were favourite subjects of miue, but since that time my investi- 

 gations have led me to attack problems related to the nadir of tem- 

 perature, and some of these I propose to consider in this discourse. 

 Our absolute scale of temperature depends on gas thermometry ; but 

 for demonstration purposes thermo junctions coupled with reflecting 

 galvanometers are more convenient. 



On lowering a thermojunction into a vessel of liquid air, the 

 galvanometer you observe registers 88° on the scale hxed on the 

 wall in degrees absolute. On blowing air through the liquid scarcely 

 any disturbance of the galvanometer is produced ; when, however, 

 hydrogen is bubbled through the liquid air, the galvanometer at 

 once shows a lowering of temperature amounting to about 5°. On 

 exhausting the liquid air, the temperature quickly falls and 70" 

 absolute is registered, and in a short time the limit of 65° is reached, 

 while the liquid air is l)oiUng under a pressure of about 2 cm. mercury 

 pressure. 



If the liquid air is now replaced by liquid hydrogen, a temperature 

 of 20° absolute is registered by the thermojunction, this being about 

 the boiling point of the liquid. When the liquid hydrogen is rapidly 

 exhausted, a fall is indicated to 14° or 15" absolute. The hydrogen 

 has now solidified under a pressure of aboat 55 mm. Continuing the 

 exhaustion on the solid hydrogen a temperature of lo|-° is indicated. 

 On admitting pure hydrogen at atmospheric pressure to the vacuum 

 vessel, the solid hydrogen melts, and a temperature of 20° is once 

 more registered. 



The temperature of 13° absolute is the practical nadir ; or the 

 lowest temperature w^e can conveniently permanently maintain by the 

 use of solid hydrogen. 



Now hydrogen boils at 20° and air at 88°, which is more than 

 four times as high. The temperature of the lecture room is about 

 300° absolute, that is fifteen times warmer than boiling hydrogen. 

 Fifteen times higher than 800° gives a temperature of 4500°, which 

 is nearly the temperature of the sun. We thus produce in the 



