230 THE SCIENTIFIC PAPERS OF 



were of a somewhat lighter hue than those exposed to daylight, 

 except in one instance when the reverse was the case ; while the 

 plants that had the benefit of both day and electric light far sur- 

 passed the others in darkness of green and general vigour. A fear 

 had been expressed that the melon and cucumber plants which 

 had been scorched by the electric light on the first evening- would 

 droop or die under continued exposure to that agency, but they 

 were replaced at a distance from the light exceeding 2 metres, and 

 they have all shown signs of recovery. A pot of tulip buds was 

 placed in this electric stove, and the flowers opened completely 

 after an exposure of two hours. 



Another object I had in view in this experiment was to observe 

 whether the plants were injured by carbonic acid, and the nitro- 

 genous compounds observed by Professor Dewar to be produced 

 within the electric arc. All continuous access of air into the stove 

 was stopped, and in order to prevent excessive accumulation of 

 heat, the stove pipes were thickly covered over with matting and 

 wet leaves. But although the access of stove heat was thus 

 stopped, the temperature of the house continued through the 

 night at 72 Fahr., proving that the electric light furnished not only 

 light, but sufficient heat also. No injurious effect was observed 

 on the plants from the want of ventilation, and it is probable that 

 the supply of carbonic acid given off by the complete combustion 

 of the carbon electrodes at high temperature, and under the 

 influence of an excess of oxygen, sustained their vital functions. 

 If nitrogenous compounds were produced in large quantities, it 

 is likely the plants would have been injured ; but they could 

 not be perceived by their smell in the stove, when all ventilators 

 were closed, and no injurious effects on the plants have been 

 observed. 



These experiments are instructive in proving that electric 

 light alone promotes vegetation, and the important fact that 

 diurnal repose is unnecessary to plant life, although the experi- 

 ments have perhaps not lasted long enough to furnish that proof 

 absolutely. We may argue, however, from analogy, that such 

 repose is not necessary, as crops grow and ripen very quickly in 

 northern latitudes, where the summer is only two months in 

 length, during which period the sun is almost altogether above 

 the horizon. 



