TESTING IN VACUO 111 



Experiment No. 2 : Much Smaller Leaf, — 



D = (in air) 90 mm. negative. Earthed ten minutes 



in vacuo. 

 D = (in vacuo) 15 mm. negative, but upon further 



pumping fell to zero. 



Experiment No. 3 : R Needle in aerolsB, L Needle in stalk, 



i.e., former connections reversed. 

 D = (in air) 90 mm. positive ; steady. Ten minutes 



earthed in vacuo, when 

 D = (in vacuo) zero. 



During the ensuing ten minutes no deflection was 

 observed upon repeated disconnection and reconnection 

 with the galvanometer. Everything was then left 

 untouched until the next morning when D = Zero. 



The bell jar was then taken off without touching 

 the electrodes and the leaf exposed to air in the dull 

 diffused light of the laboratory for one hour without any 

 change taking place. The leaf was then placed in the 

 open air — occasional sunshine — for half-an-hour, the 

 Needles replaced as before and a fresh observation made. 

 D = (in air) 70 mm., but fell in five minutes to zero. 



It was then given three hours' open-air exposure 



when 

 D (immediate) = 150 mm., but fell in five minutes to 



zero and thereafter gave no response. 



Experiment No. 4 : Apple cut in section, and wiped to 

 prevent diffusion. 



D = (in air) 190 mm. +. 



After ten minutes earthed in vacuo, 500° shunt 



D = (in vacuo) Zero. 



Note : Went negative after a time, due to earth- 

 current. 



Experiment No. 5. — Laurel Leaf. 

 D - (in air) Off Scale. 



After forty minutes earthed in vacuo 

 D = (in vacuo) Zero, 



