inserting, before the arm strikes the top. The 

 side arm is long enough so that the straight 

 part of it more than holds the mercury column, 

 when desired, and at the same time short 

 enough so that when in position it lies about 

 half an inch below the shoulder of the reservoir 

 bottle. The proper dimensions can readily be 

 ascertained by the use of a cardboard model 

 and a bottle of the type it is intended to use 

 as the reservoir. The glass tubing should be 

 of sufficiently large bore to permit the ready 

 passage of large air bubbles. 



In setting up the apparatus the feed tube is 

 first shoved through the reservoir stopper from 

 below and the atmometer stopper affixed to its 

 upper end in the usual way. Next, enough 

 mercury is placed in the crook at the bottom 

 of the tube to completely block the passage. 

 The whole thing is then carefully turned up- 

 side down, in such a way that the mercury col- 

 umn runs out of the J and into the side-arm. 

 With mercury and tube in this position the 

 atmometer, filled with water, is attached (or it 



