228 THE SCIENTIFIC PAPERS OF 



open air a regulator contained in a lamp having a metallic re- 

 flector, about 2 metres above the roof of a sunk melon house. 

 Several pots were provided, and planted with quick-growing seeds 

 and plants, such as mustard, carrots, melons, &c. The plants were 

 arranged to be brought at suitable intervals, without moving them, 

 under the influence of daylight and electric light, both falling upon 

 them at approximately the same angle. The pots were divided 

 into four groups or series. One group was kept entirely in the 

 dark, another was exposed to the influence of electric light only, 

 the third to the influence of daylight only, and the fourth was 

 exposed successively to both day and electric light. 



In this first trial the electric light was supplied during six 

 hours, from 5 to 11 each evening, the plants being left in darkness 

 the rest of the night, but in experiments hereafter to be referred 

 to, the electric light was kept on during the whole night. 



In every instance the differences of effect were unmistakable. 

 The plants kept in the dark were pale yellow, thin in the stalk, 

 and soon died. Those exposed to electric light only, showed a light 

 green leaf, and had sufficient vigour to survive. Those exposed to 

 daylight only were of a darker colour and greater vigour. Those 

 exposed to both sources of light evinced a decided superiority in 

 vigour over the rest, and the colour of the leaf was a dark rich 

 green. 



It must be remembered that in this trial of electric against 

 solar light, the period of exposure was in favour of the latter in 

 the proportion of nearly 2 to 1, but after making every allowance, 

 the average daylight in these latitudes in the early portion of 

 the year appears to have about twice the effect of electric light. 

 It was evident, however, that the electric arc was not so placed 

 as to give out its light to the greatest advantage. The nights 

 were cold, and the plants under experiment were for the most 

 part of a character to require a hot moist atmosphere ; the glass 

 thus became covered very thickly with moisture, obstructing 

 thereby the action of the light, besides which the electric light 

 had to traverse the glass of its own lamp. Notwithstanding these 

 drawbacks, the electric light clearly formed chlorophyll and its 

 derivatives in the plants. But it was, besides, interesting to 

 observe the mechanical action that took place, for the mustard 

 seed stem, when placed obliquely, turned completely towards the 



