Oct. 18. 191S 



Automatic Transpiration Scale 



123 



Ball-dropping device. — The ball-dropping device used in our experi- 

 ments is shown in fig. 12. A commercial telegraph sounder provides 

 an efiacient mechanism for actuating the valve. When the circuit is 

 closed, the slide A moves in the direction of the arrow and releases the 

 lowest ball in the tube. The remaining balls are prevented from pass- 

 ing down the tube by the upper septum B, which moves into the tube as 

 the lower septum C moves out. When the circuit is broken, a spring 

 restores the valve mechanism to its original position and the reserve 

 balls slide down the tube so as to rest against the lower septum. The 

 mechanism is now in 

 position to drop 

 another ball as soon as 

 the circuit is again 

 closed. 



As the discharged 

 ball leaves the valve it 

 drops into the bal- 

 anced receptacle D, 

 which tips downward 

 under the weight of the 

 ball, closing the circuit 

 of the recorder through 

 the mercury cups E be- 

 low. The ball in the 

 meantime rolls into the 

 funnel and is delivered 

 into the ball receiver L 

 suspended from the 

 balance beam. With 

 this arrangement no 

 record is made unless 

 the ball is actually re- 

 ceived in D, and a second ball can not be recorded until the first has 

 been delivered and D has returned to its initial position. In very gusty 

 weather there is occasionally a fluttering of the valve A, two balls being 

 dropped in rapid succession. The second ball simply shoots over D 

 into the waste cup and is not recorded. 



The tube holding the reserve supply of balls (fig. 11) is of glass bent 

 into the form of an open spiral, and is joined to the valve tube by a 

 conical adapter. The diameter of the valve tube at the septa must be 

 only slightly greater than the diameter of the balls to insure the valve's 

 working properly, and the tube should taper gradually to this diameter. 

 The distance between the adjacent faces of the two septa should also be 

 equal to the diameter of the ball. Each septum when in its intercepting 



Fig. 9.— Copeland's apparatus for recording transpiration in which 

 the loss in weight through transpiration is counterbalanced by a 

 change in position of a partially submerged float. 



