1880.] Influence of Electric Light upon Vegetation. 211 



radiation, which, inquiries were not however carried far enough to 

 furnish absolute results. They served me, however, for a stepping 

 stone to the subject of my present communication. 



The vast development of vegetation proves that dissociation is 

 accomplished freely within the leaf-cells of plants, in which both water 

 and carbonic acid are broken up in order that chlorophyl, 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 Pre- 

 sident of the Royal Society, that I thought the electric arc might bo 

 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 I have since that time gradually matured a plan for 

 conducting the experiment. Operations were commenced only at the 

 beginning of the year, and although the results are necessarily in- 

 complete, they are nevertheless sufficiently positive and remarkable to 

 make them perhaps acceptable to the Royal Society as a preliminary 

 communication on the subject. I was induced to look for interesting- 

 results in these experiments on account of the great abundance of 

 blue and actinic rays in the electric arc, upon which its value in 

 photography depends. In experimenting with powerful electric lamps 

 for illuminating purposes, I have been struck moreover by the action 

 produced upon the skin, which is blistered, without the sensation of 

 excessive heat at the time, an effect analogous to that produced by 

 solar rays in a clear atmosphere. 



Effect of Radiant Energy on Plants. 

 The apparatus which has been put up at Sherwood consists — 1. Of a 

 vertical Siemens dynamo-machine, weighing 50 kilos., with a wire re- 

 sistance of - 717 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. 



