214 



Dr. C. W. Siemens. 



[Mar. 4, 



cucumber plants, which had been scorched by excess of electric light 

 on the first evening, would droop or die if further exposed to that 

 agency, but I insisted upon their being placed within the influence of 

 the electric light, at a distance from it exceeding 2 metres, and all 

 of them have shown signs of recovery, throwing out fresh leaves and 

 pearls of moisture at their edges. A pot of tulip buds was placed in 

 this electric stove, and the flowers were observed to open completely 

 after two hours' exposure. 



One object I had in view in this experiment, was to observe whether 

 the carbonic acid and nitrogenous compounds produced within the 

 electric arc exercised any deleterious action upon the plants. All con- 

 tinuous access of air into the stove was closed, and in order to prevent 

 excessive accumulation of heat, the stove pipes were thickly covered 

 with matting and wet leaves. But although the access of stove 

 heat was thus virtually stopped, the temperature of the house was 

 maintained throughout the night at 72° F., proving that the electric 

 lamp furnished not only a supply of effective light, but of stove beat 

 also. No hurtful effect was moreover observed on the plants from the 

 want of ventilation, and it would appear probable that the supply of 

 pure carbonic acid resulting from the complete combustion of the 

 carbon electrodes at high temperature, and under the influence of an 

 excess of oxygen, sufficed to sustain their vital functions. If the 

 nitrogenous compounds which Professor Dewar has shown to be de- 

 veloped in the electric arc were produced in large quantities, injurious 

 effects upon the plants must undoubtedly ensue, but it can be shown 

 that in a well- conditioned electric lamp, with a free circulation of air 

 round the carbon electrodes, the amount of these products is ex- 

 ceedingly small, and of a different nature than is produced in a con- 

 fined space. They could not indeed be perceived by their smell in 

 the stove, when all ventilators were closed, and no injurious effects 

 from them have hitherto been observed in the plants. 



These experiments are not only instructive in proving the sufficiency 

 of electric light alone to promote vegetation, but they also go to prove 

 the important fact that diurnal repose is not necessary for the life of 

 plants, although the duration of the experiments is too limited perhaps 

 to furnish that proof in an absolute manner. It may, however, be 

 argued from analogy, that such repose is not necessary, seeing that 

 crops grow and ripen in a wonderfully short space of time in the 

 northern regions of Sweden and Norway, and Finland, where the 

 summer does not exceed two months, during which period the sun 

 scarcely sets. 



The next step in the course of these experiments was to remove the 

 electric lamp into a palm house, constructed of framed glass, which was 

 2$ ft. 3 in. long, 14 ft. 6 in. wide, and averaging 14 ft. 6 i . 

 (8*62 m. x 14*42 m. X 4*42) in height. In the centre of this house 



