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CHAPTER VII 



THE MERCURY VAPOUR LAMP 



IN the winter of IQIO to Spring, 1911, I experimented with the 

 mercury vapour lamp, which was, I believe, the first time that it 

 had been applied to electro-cultural experiments in this country. 

 This lamp consists of a long glass tube about an inch in diameter, 

 with a bulb at the end containing a small quantity of mercury. 

 When the electric current is switched on the lamp tilts, sending 

 the mercury along the tube till it makes contact with the wire 

 conveying the electric current at the other end. It then automa- 

 tically returns to its former position, part of the mercury becoming 

 vapourised as it runs back which gives a curious bluish yellow 

 light as long as the electric current is kept on. 



The house in which the experiment was tried was about 2oft. 

 x loft., a smaller house being kept as a control house. The first 

 trial was to see the effect of this lamp upon the germination of 

 seeds, some British and some foreign ones being planted on 

 December jth in 6in. pots, and one of each variety placed in both 

 houses. Under the influence of the light germination commenced 

 much more quickly in the experimental than in the control house, 

 as the following table will show : 



EXPERIMENTAL. 



CONTROL. 



The temperature of the two houses was kept as nearly as pos- 

 sible the same, also the temperature of the soil, the readings of 

 the thermometer were taken each morning at 9 a.m. The control 



