1920] 



on Low Temperature Studies 



247 



fine needle, a steady jet of water was obtained, the upper limit of 

 which was projected on the screen. On pouring warm water over 

 the balloon, the resultant tightening of the rubber was shown by a 

 sudden rise in the height of the water jet. 



(2) Elasticity of rubber membrane in liquid air and at ordinary 

 temperatures. An empty metal capsule 4 cm. diameter, covered by a 

 membrane, was connected to a U-manometer, and its scale projected 

 on the screen. A 5 cm. light watch glass rested on the membrane 

 without appreciable distortion. When loads increasing up to 200 

 grammes were placed on the watch glass, corresponding displace- 

 ments of the manometer were obtained, increasing uniformly up to 

 15 cm. pressure (alcohol). This experiment was repeated after 

 cautiously and gradationally cooling the capsule in liquid air. The 



Strength of 

 Rubber Membrane 



ioo 

 Crms Load 



Fig. 2. 



resulting displacements for the same loads reached only 8 cm., but 

 were still quite regular, as shown in Fig. 2. 



(3) Membrane impervious at low temperatures. This experiment 

 was first shown in the Discourse of June 5, 1908." An india-rubber 

 membrane was stretched and bound over the end of a piece of glass 

 tube about 2 cm. diameter, to which was sealed an ordinary discharge 

 tube and charcoal bulb with stopcock. The membrane was 

 cautiously cooled and immersed in liquid air. and the apparatus 

 whs exhausted by opening the charcoal stopcock. The vacuum was 

 then too high for a discharge to pass, and remained so when the 

 charcoal was shut off. When the membrane was cautiously warmed 

 up by steadily lowering the liquid'air vessel in which it was immersed, 

 air began to pass through the membrane and the discharge started. 



Proc. Roy. Inst., xix. p. 417. 



