MARIAN IRWIN 



205 



slipped over the glass for about 1 inch and cemented to the glass by 

 soft de Khotinsky cement. V and Vi show the position of the valves, 

 which allow the air to pass in one direction only (from Z to W) . The 

 valves are made of thin rubber sheeting attached to perforated rubber 

 stoppers. 



In order to produce a circulation of air the piece of rubber tubing is 

 alternately compressed and released by means of the device shown in 

 Fig. 2. The motor operates a cam the turning of which causes the 



Fig. 2. The motor turns a cam which causes the horizontal arms alternately 

 to approach and separate, thus compressing a piece of rubber tubing and main- 

 taining a circulation of air in the apparatus. 



two horizontal arms alternately to separate and to approach each 

 other (they are held together by a vertical spring at the right of the 

 cam^). Two projections at the ends of these arms are adjusted so as 

 to compress the rubber tubing to the proper degree. The arms are 

 made so that the height and the angle can be adjusted. The writer 

 prefers a speed of 120 compressions per minute (the speed of the 

 motor is reduced by gears). 



** A worm may be substituted for the cam if noiseless operation is desired. 



