338 Dr. G. William Siemens [March 12, 



would be produced in the latter case. In practical working, the 

 difference would not be so great, owing to the imperfect arrange- 

 ments as yet adopted ; but he could show, from actual experience 

 extending over several months, that electric illumination if applied 

 to halls, and places of a certain magnitude, was three or four times 

 cheaper than gas lighting. 



The application of the dynamo-electric current next dealt with 

 was that of the fusion of metals and other substances. Sir Humphry 

 Davy had as early as 1810 obtained in the electric arc sufficient heat 

 to decompose potash, and Professor Dewar in experimenting with the 

 dynamo-electric current had shown recently that in his lime tube or 

 crucible several of the metals assumed the gaseous condition as 

 shown by the reversal of the lines in his spectrum, thus proving that 

 the heat obtained by him was not much inferior to solar heat. 



The lecturer had experimented for some time with an electric 

 furnace, not with a view of attaining these extreme degrees of heat, 

 but rather with the practical object of melting such refractory 

 materials as platinum, iridium, and steel in considerable quantities. 

 He was led to these experiments by the consideration that a good 

 steam engine converted nearly 15 per cent, of the heat energy residing 

 in coal into mechanical effect, and that by the dynamo-electric machine 

 nearly 80 per cent, of that mechanical energy could be converted 

 into electric energy. If this could be expended without loss within 

 an electric furnace or crucible, 12 per cent, of the total energy 

 residing in the coal would be conveyed to the refractory material to 

 be melted at any degree of temperature required, and such a result 

 would far exceed in economy that of the best furnaces yet 

 constructed. 



In the small furnace placed before the meeting, the positive 

 electrode (of iron) entered from below a crucible containing the 

 metal to be melted, whereas the negative electrode was in the shape 

 of a rod of carbon, or of a metal tube cooled by a current of water, 

 which, descending through the crucible cover, was attached by means 

 of a lever to a solenoid regulator. The crucible was packed in char- 

 coal or other non-conducting material contained in a copper vessel to 

 prevent loss of heat, and so great was the heat accumulated within 

 the crucible, that in the course of about twenty minutes a kilogramme 

 of broken files was completely melted. The arrangement was such 

 that it could easily be applied upon a larger scale, and electric fusion 

 had the great advantage that the access of the atmosphere and of the 

 products of combustion to the substance under treatment was entirely 

 prevented. 



Another application of the electric arc which the lecturer thought 

 might ultimately assume an important character was to horticulture. 

 Having experimented with an electric light of 1400 candle power in 

 his own greenhouses at Sherwood, near Tunbridge Wells, he had 

 arrived at the conclusions that electric light promoted the formation 

 of chlorophyll, starch, and cellulose in plants, and could be made 



