Automatic Transpiration Scale 



125 



Spring motor for raising beam. — The dropping of a ball into the 

 receiver is ordinarily sufficient to raise the opposite end of the beam 

 and open the circuit. It sometimes happens, however, when the trans- 

 piration rate is high and a gusty wind is blowing, that the beam remains 

 down until the transpiration has been sufficient to require a second ball 



Fig. II. — View of the beam and atixiliarj' equipment of the platform transpiration scale designed to carry 

 large pots of plants weighing 150 kgm. or more. As the plant loses weight, the beam falls and the plat- 

 inum point P closes a circuit through the mercury cup U. This actuates the ball dropper A, which 

 deposits a ball in the receiver L. At the same time the cam K makes one revolution, raising the beam 

 to its upper position and leaving it free to fall. An oil dashpot is provided at O. 



to counterbalance the loss in weight. Under such conditions the balance 

 would fail to operate without the inter\'ention of some protective device. 

 This protection is secured by a spring motor which raises the beam to 

 its upper position each time a ball is dropped and then leaves the beam 

 free. The motor, which consists of a strong 8-day clock movement 

 equipped with a fan, F (fig. 14), to reduce the speed, is controlled by 



