1880.] Influence of ElectAc Ligl it upon Vegetation. 217 



at which to place the naked electric light of 1,400 candle-power is 

 about 2 metres. By providing a metallic reflector, and thus throwing 

 the major portion of the upward rays down upon the surface to be 

 illuminated that height may be taken at 3 metres. If the electric arc 



employed was equal to 6,000 candles, the height would be ^^522x3 



= 6'2 metres, at which such an electric light should be fixed under the 

 protection of a tin plate or other reflector. In operating upon an ex- 

 tended surface several lamps should be placed at such distances apart, 

 as to make the effect over it tolerably uniform. The effect of radiation 

 would be equally distributed over the ground if the radiating centres 

 were placed at distances apart equal to double their height above the 

 ground ; for under these circumstances a square foot of surface mid- 

 way between them would receive from each centre one-half the number 

 of rays falling upon such a surface immediately below a centre. A 

 plant at the intermediate point would, however, have the advantage 

 of presenting a larger leaf surface to the two sources of light ; and in 

 order to compensate for this advantage, the light centres may be 

 placed considerably further apart, sa}^ at distances equal to three times 

 their elevation, or 18 metres. Nine lights so placed would cover an area 

 54 metres square, or just about f acre. If this space was enclosed 

 with a high fruit wall (as shown with the lamp centres marked in the 

 accompanying sketch), this will also get the full benefit of electric 



radiation, and would serve at the same time to protect the plants froni 

 winds. Protection against injury from this latter cause might be 

 further carried out with advantage by following plan adopted (with 

 excellent results I believe) by Sir William Armstrong, that of sub- 

 dividing the area under forced cultivation by vertical partitions of 

 glass. 



The engine-power necessary to maintain this radiant action would 

 be 9x4=36 horse-power, involving the consumption of 36x2| = 

 90 lbs. of fuel per hour, or say, for a night of 12 hours (with an 

 allowance of 40 lbs. for getting up steam) 10 cwt., which, at sixteen 

 shillings per ton, would cost eight shillings. This expenditure would 

 not include, however, the cost of carbons and of an attendant, which 

 would probably amount to another eight shillings, making a total of 



