250 



ANNUAL, EEPORT SMITHSONIAN INSTITUTION, 193 5 



I will begin by showing two experiments. The first is the pro- 

 duction of a high temperature. It is a very simple experiment that 

 3^ou have all done yourselves. I need only switch on an electric 

 lamp. By varying the current I get temperatures up to 2,500°. 



In the second experiment I will generate a very low temperature, 

 and that is much more complicated. While I could certainly per- 

 form the first experiment without any help, the second would be 

 impossible without the kind help of Mr. Green, Dr. Kiirti, Dr. Lon- 

 don, and the staff of the Clarendon Laboratory, who have all helped 

 in its preparation. We will now liquefy helium, making use of a 



100 -- 373 BOILING Pi H.O 



15 

 



83 

 95 



-253 



-269x 



-273- 



288 ROOM TEMP. 

 273 MELTING Pi H,0 



90 BOILING P'- Oj 

 78 BOILING PS N, 



V /20 BOILING P5 H2 

 -K A BOILING Ps He 

 ■' 



HELIUM REGION 



^K 



5-2 -- CRITICAL Ps 



4-2 -- BOILING Pi 



Figure 1. 



0-7 + KEESOM 

 



FiGUKB 2. 



principle about which I will say something later. Now, I should 

 like to point out that we start at a temperature obtained with solid 

 hydrogen (about 12°) , that within the apparatus there is helium com- 

 pressed to about 100 atmospheres at this temperature, and that the 

 helium will be expanded into a balloon, where we will store it. Dur- 

 ing the expansion the helium will liquefy and reach its boiling tem- 

 perature, 4.2°. As the helium is enclosed in a metal vessel, I will 

 not be able to show it to you, but even if I could, it would not look 

 a bit colder than liquid air. This simplified gas thermometer gives 

 you a much better measure for the temperature. You saw that it 

 pointed first to 12° then, as the helium was expanded and this 



