456 



NATURE 



[March n, 1880 



of the German dealers in wild bea-ts. Many German travellers 

 originally started from here on their tours, such as Florian, 

 Werner, Cohn, Dr. Schweinfurth, Heuglin. Dr. Mook and 

 Baron Holzhausen intend to move in a south-easterly direction 

 towards the Rahat and Diuder. 



The German Government has supported African research 

 with the sums of 100,000 marks (5,000/.) during 1878, and 

 70,000 marks (3,500/.) during 1879. For the present year it is 

 proposed to devote anothersumof 70,000 marks to this purpose, 

 besides a sum of 5,000 marks (250/.) for the furtherance of 

 independent private research in the Dark Continent. 



THE Paris Municipal Council has held a secret sitting to 

 deliberate upon the organisation of a great banquet to Prof. 

 Nordenskjold. It has been decided that a gold medal be pre- 

 sented to the explorer in the Salle des r.tats. 



The municipal authorities of Gossen^ass, on the Brenner 

 Railway, have re-christened the Hiinerspiel peak, famous for the 

 magnificent view which is obtained from its summit, and « hich 

 lies within their district. The peak will henceforth be callrd 

 Amthorpeak, in honour of Dr. E. Arnthor, of Gera, an eminent 

 " Alpine" writer. 



ON THE INFLUENCE OF ELECTRIC LIGHT 

 UPON VEGETATION AND ON CERTAIN 

 PHYSICAL PRINCIPLES INVOLVED* 



"THE vast development of vegetation proves that dissociation 

 ■*■ is accomplished freely within the leaf-cells of plants, in 

 which both w ater and carbonic acid are broken up in order that 

 chlorophyll, starch, and cellulose may be formed. It is well 

 known that this reaction depends upon solar radiation ; but the 

 question may fairly be asked whether it is confined to that 

 agency, or whether other sources of light and heat, which, in 

 common with the sun, exceed the temperature of dissociation, 

 may not be called into requisition, in order to continue the action 

 of growth, when that great luminary has set or is hidden behind 

 clouds ? 



About two years ago I mentioned to Sir Joseph Hooker, then 

 President of the Royal Society, that I thought the electric arc 

 might be found sufficiently powerful to promote vegetation and 

 that I should be willing to undertake some experiments on the 

 subject if he could give me any hope of confirmative results. 

 Sir Joseph Hooker gave me sufficient encouragement to induce 

 me to follow up the subject, and 1 have since that time gradually 

 matured a plan for conducting the experiment. 



The apparatus which lias been put up at Sherwood consists— 

 I. Of a vertical Siemens dynamo-machine, weighing 50 kilos, 

 with a wire resistance of 0717 unit on the electro-magnets. 

 This machine makes 1,000 revolutions a minute, it takes 2 horse- 

 power to drive it, and develops a current of 25 to 27 webers 

 of an intensity of 70 volts. 2. A regulator or lamp, constructed 

 for continuous currents, with two carbon electrodes of 12 

 millims. and 10 millims. diameter respectively. The light 

 produced is equal to 1,400 candles measured photometrically. 

 3. A motor, which at present is a 3 horse- power Otto gas-engine, 

 but which it is intended to supersede by a turbine to be worked 

 by a natural supply of water, at a distance of about half a mile 

 from the house. 



My object in making these experiments was to ascertain 

 whether electric light exercised any decided effect upon the 

 growth of plants. For this purpose I placed the regulator in 

 a lamp with a metallic reflector, in the open air, about two 

 metres above the glass of a sunk melon house. A consider- 

 able number of pots were provided, sown and planted » ith 

 quick-growing seeds and plants, such as mustard, carrot-, 

 swedes, beans, cucumbers, and melons. The plants could then 

 be brought at suitable intervals under the influence of daylight 

 and electric light, without moving them, both falling upon them 

 approximately at the same angle. The pots were divided into 

 four groups. 



1. One pot of each group was kept entirely in the dark. 



2. One was exposed to the influence of the electric light only. 



3. One was exposed to the influence of daylight only. 



4. One was exposed successively to both day and electric 

 light. 



The electric light was supplied for six hours, from 5 to 11 



1 Abstract of a paper read at the Royal Society on March 4, by C. William 

 Siemens, D.C.L., F.R.S. 



each evening, all the plants being left in darkness during the 

 remainder of the night. 



In all cases 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 green and greater vigour. 

 Those exposed to both sources of light showed a decided 

 superiority in vigour over all the others, and the green of the 

 leaf was of a dark rich hue. 



It must be remembered that, in this contest of electric against 

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

 the proportion of nearly two to one, but all allowance made, 

 daylight appeared to be about twice as effective as electric light. 

 It was evident, however, that the electric light was not well 

 placed for giving out its power advantageously. The nights 

 being cold, and the plants under experiment for the most part of 

 a character to require a hot moist atmosphere, the glass was 

 covered very thickly with moisture, which greatly obstructed the 

 action of the light, besides which, the electric light had to pass 

 through the glass of its own lamp.' Notwithstanding these 

 drawbacks, electric light was clearly sufficiently powerful to 

 form chlorophyll and its derivatives in the plants. 



These preliminary trials go to prove that electric light can be 

 utilised in aid of solar light by placing it over greenhouses, but 

 the loss of effect in such cases must be considerable. I, there- 

 fore, directed my observations, in the next place, to the effect ( f 

 electric light upon plants, when both were placed in the 

 apartment. The plants under experiment were divided into 

 three groups ; one group was exposed to daylight alone, a second 

 similar group was expo ; ed to electric light during eleven hours of 

 the night, and were kept in the dark chamber during tk; day 

 time, and the third similar group was exposed to eleven hours' 

 day and eleven hours' electric light. These experiments were 

 continued during four days and nights consecutively, and the 

 results observed are of a very striking and decisive character, as 

 regards the behaviour of such quick-growing plants as mustard, 

 carrots, &c. The plants that had been exposed to daylight alone 

 (comprising a fair proportion of sunlight) presented their usually 

 healthy green appearance ; those exposed to electric light alone 

 were, in most instances, of a somewhat lighter, but, in one 

 instance, of a somewhat darker hue than those exposed to day- 

 light ; and all the plants that had the double benefit of day and 

 electric light far surpassed the others in darkness of green and 

 vigorous appearance generally. A pot of tulip buds w.i 

 in" this electric stove, and the flowers were observed to open 

 completely after two hours' exposure. 



Although the access of stove heat was virtually stopped, the 

 temperature of the house was maintained throughout the night 

 at 72" F., proving that the electric lamp furnished not only .-. 

 supply of effective light, but of stove heat 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 carbonic electrodes at high temperature, and under the in- 

 fluence of an excess of oxygen, sufficed to sustain their vital 

 functions. If the nitrogenous compounds which Prof. Dewar 

 has shown to be developed in the electric arc were produced in 

 ■large quantities, injurious effects upon the plants must undoubt- 

 edly 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 exceedingly small, 

 and of a different nature than is produced in a confined space.^ 



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, w^here the sum- 

 mer 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 2S feet 3 in. long, 14 feet 6 in. wide, and averaging 



1 Prof. Stokes has shown, in tSs7. th« the electric arc is particularly rich 

 in highly refrangible invisible r.iys, a circumstance which seems to point to a 

 great loss on passing those rays through glass. 



