414 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



with the exception of the heat losses in the gas generator, every available 

 heat source both of exhaust gases (as sensible heat) and of jacket water 

 (as sensible heat) is utilised, securing a useful efficiency of 90 per cent. 



The actual programme of the experimental machine includes not 

 only the jacket-water service and the exhaust-gases service for heating 

 the glass house and for adding moisture to the air, but also the air from 

 around the gas plant. The heated air is circulated by an electric fan, 

 which also diffuses the water vapour. The arc light travels on a special 

 electric traveller backwards and "forwards along the length of the house, so 

 as to secure as near a resemblance as practicable to actual solar effect. 

 The rays are reflected through a water or double-glass screen, so that 

 the rays are subdued, the red ray effects being modified and allowing freer 

 play for the effect of the violet or actinic rays (fig. 07). 



Fig. 68. — Stimulated Plants on kight ; Nokmal on left. 



A chimney is provided on the hood for removing the oxides of 

 nitrogen that may be produced by the arc. The programme of operations 

 includes as a second stage the pari passu application of the electro- 

 static influence overhead discharge, but intermittently into the lamps and 

 direct to the soil. 



The third stage will include the addition of carbon dioxide isolated 

 from the exhaust gases to the extent to increase the proportion to the 

 optimum extent or 3 per cent. 



An objection that may be raised is the possibility of the entrance of 

 carbon monoxide into the glass house. According to the interesting 

 experiments of W. B. Bottomley, if CO displaces C0 2 in proportion 

 to their relative solubilities in water, or with twenty times as much 

 CO as C0 2 , the plants remain healthy and normal ; with a CO environ- 

 ment starch is formed when plants are exposed to sunlight during three 



