( 203 ) 



The cause of those deviations has not been explained. In a ease 

 where a particularly large deviation had been stated which did not 

 altogether return to zero, it appeared, when the points were un- 

 wrapped, that a rift had come into the glass. 



To see whether a thermical hysteresis had come into play a 

 thermometerbulb (see fig. 1) witii a tine capillary tube was filled 

 with mercury. First the level of the mercury was compared with 

 an accurate thermometer at the temperature of the room in a water- 

 bath in a vacuum glass. Then the apparatus was turned upside down 

 so that the mercury passed into the reservoir B, which is a little 

 greater than A. Subsequently.! and also a part of the stem was cooled 

 down during 3 hours in liquid air in a sloping position so that thanks 

 to the capillary being bent near B no mercury could flow back 



TABLE I. — JENA GLASS 16 1". 



