This section is from the book "The Gardener V3", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
SUCH of your readers as may have seen the observations made by me in your number for July 1880, and felt any further interest in the question, will probably be expecting to hear whether any progress has since been made in the application at Sherwood of electric light to horticulture; and I regret to have to say that, in my judgment, no progress has been made towards a successful application of it.
There has been in use since December last, until about ten days ago, a larger electric lamp than the one used last year, with an illuminating power equal to 4000 candles, enclosed in a glass globe, to prevent wind blowing it out, hoisted on to the top of a high mast placed outside of, but almost touching the low-pitched Melon and Cucumber house, which I call No. 1; and in a square glass house, which I call No. 2, at one end of, and close to the roof, there is a small electric light enclosed in a glass casing, with a zinc chimney-like opening into the external air, to allow of the noxious products of combustion passing off. The steam-engine which sets in motion the dynamo-electric machine is much larger than the one previously in use, and, in fact, during the day is employed in transmitting power through an electric continuator to the farm, where chaff-cutting, turnip or wood cutting may be carried on.
The electric light has been, during the period alluded to, applied to both of these houses, from the hours of six o'clock p.m. to six o'clock a.m. I incline to think that there is no appreciable increase of temperature of atmosphere beyond the distance of about a foot from the electric light; but so many changes by way of experiment have been made during the period alluded to, that it would not be just to consider that either in house No. 1 or in house No. 2 has it yet had a fair trial.
My object is not to criticise the work, but rather to draw attention to some of the results originally expected, and to consider how far they are likely to be realised.
It was suggested by its promoters that the provision of the alternate influence of light and darkness during the twenty-four hours was not necessary for plant-life. That, by the aid of electric light, the colouring matter of chlorophyll in the leaves of the plant could be produced; that it aids the growth of plants; that it will counteract the effects of night frosts, and will promote the setting and ripening of fruit in the open air. That plants when growing continuously, as in the arctic (northern was intended) summer, develop more brilliant flowers, and larger and more aromatic fruits, than when grown under the usual old-fashioned way of light, followed by its diurnal absence or darkness. Now let us try and consider how the matter really stands.
1. Light and heat (whatever their physical differences may be) always travel together in lines or rays, as they are called, from the sun to the earth. Their joint use in plant-life is supposed to be fairly understood and appreciated; but it is not so easy to say accurately whether one of them, separated from its companion, is a more active promoter of any function of plant-life than the other. But when light and heat are made to travel by different routes, and arrive at the plant-house by different vehicles (excuse the word), as light by the electric lamp, and heat by the hot-water apparatus, it is hardly safe to conclude that they will do the work as well as when harnessed together as in a sunbeam.
2. Supposing the plants of the northern (not arctic) summer to be similar to those that horticulturists here would wish to grow, it does not follow, even if continuous light - that is, solar light, followed on by electric light - had been applied during our summer months when the temperatures of the external atmosphere of air and of soil would have been more congenial to plant-life, that the same results of a northern summer would have been obtained here, even if these results are desirable. They were stated by Dr Schubeler in effect to be - that the further north we go within certain fixed limits, the more energetic is the development of the pigment in flowers, leaves, and seeds; while the aroma of wild and cultivated fruits is much greater than that of the same fruits in more southern countries, but that this excess of aroma coexists with an inferior degree of sweetness. Such of us as are gardeners will at once see that one of the important factors in the question is the wood being well ripened during the northern summer; another, the inspissated state of the sap of the plant, probably arising from the dry state of the atmosphere; and a third is long rest during the northern winter, and the absence of heat, - any of which would go a long way to account for the results of the northern summer, without entirely giving the continuous light of the summer the credit of them.
3. The application of continuous light - that is, solar followed on by electric light - however applied, whether outside or inside during the low temperatures of soil and of atmosphere, of our winter months, is not likely to be productive of high-coloured flowers, and of fruit with high aroma.
4. Again, as to the statement that electric light produces green colouring matter in chlorophyll corpuscles, that may, or may not, be correct; but in any experiments made after the absence of solar light with the electric light, who is to decide whether the green colouring matter is not due to the action of solar light during the daytime, rather than to the action of electric light during darkness? Here I would remark that chlorophyll is not now considered to have any power to decompose carbonic acid (carbon dioxide); it only absorbs or quenches some of the solar rays, allowing others to pass on to where the protoplasm is at work, which, with the aid of these rays, alone possesses the power to decompose its own food-material (carbon dioxide).
5. As to the electric light aiding growth, it hardly applies, as plants grow in darkness. The question is, whether it does enable a plant to assimilate its food, ripen its wood, and otherwise perform its functions.
Upon a careful consideration of the whole matter, I think the following are fair observations to make : -
6. So far as regards the primary question as to whether the provision by the Creator, of alternate light and darkness during the twenty-four hours in our climate, can be dispensed with by plants, I doubt it. It may be possible to interfere with it for short limited periods, as for forcing or for growing short-lived plants, as Melons or Cucumbers.
7. So far as an application of electric light during the winter months to counteract night frosts to outdoor wall fruit-trees, or an application of electric light in the spring to outdoor wall fruit-trees, after they have been started naturally by solar light and heat into growth, and continued on during darkness by electric light until the fruit is ripe, I give no opinion until they are tried.
8. So far as regards its application during the winter months by the outside electric light to the cultivation of Melons and Cucumbers, grown inside a house heated with hot-water apparatus as in house No. 1, the results are not at present such as to warrant any favourable expectation from its adoption.
9. So far as regards its application during the winter months by means of an electric lamp placed inside the house, as in house No. 2, specially glazed in to prevent injury to the plants, in which case the light might be said to assume the appearance, if not the characteristics, of daylight, I do not give any opinion until it has been fairly tried.
10. So far as regards any form of application during the summer months, I do not give any opinion until it has been tried.
11. In my simplicity I previously suggested that it would have been desirable for horticulturists to have had two houses similar to No. 1 house started at the same time - one of them treated in the usual old-fashioned way, with alternate light and darkness, and the other treated with solar light by day and electric light by night, but both of them heated with hot-water apparatus, and the work respectively done by them properly compared and measured up. I regret to have to say there is no probability of that being adopted.
12. So far as regards a combined application of electric light as a motive power to purposes of horticulture as well as agriculture, it is not desirable for many reasons, into which it is not worth while entering.
At present the electric light at Sherwood has ceased burning, and its consideration by me stands adjourned to another year (D. V).