20 Electricity as an Illuminant. 



of the electric light, exhibited a number of photographic slides 

 showing the various appliances used in the production of the 

 light at the various periods of its history. He then described 

 the different systems of using the electric current for lighting, 

 and proceeded : — 



The alternating current is now employed in lieu of an in- 

 terrupted direct current, because it is more powerful in its 

 effects, and presents far less difficulty in its management than 

 would arise from the break in a high tension current. The 

 direct current method, however, may be adapted to high, 

 medium, or low pressures, according to the area which it has 

 to supply and the distance at which the generating station is 

 placed. For comparatively small sections, more especially 

 where the generating station can be placed pretty near to the 

 area to be lighted, the low pressure direct system can be em- 

 ployed, and if the three-wire plan, patented by Dr. Hopkinson 

 in 1882, is adopted, a saving of 40 to 50 per cent, in the weight 

 of the cables can be effected. It is a controverted question, 

 however, which is the best system for central station supply. 

 Each has its advantages under certain conditions. There is no 

 doubt that for great distances the high-pressure alternating 

 currents, with transformers capable of reducing the pressure at 

 once or by steps, offer many and perhaps almost overwhelming 

 advantages. At Frankfort-on-the-Main last year the current 

 for lighting a great many lamps at the Exhibition was 

 generated at Lauffen-on-the-Neckar, distant 108 miles. It 

 is notable that in this instance the current is generated by 

 the dynamo at the low pressure of 50 volts and 4,000 amperes, 

 requiring for this purpose about 300 horse-power, which is 

 supplied by a turbine worked by the falls of the river. This 

 low-pressure current passes immediately through a transformer, 

 which raises the pressure of the current to 16,000 volts, but with 

 a corresponding reduction in the amperes, and the transformed 

 current is then conveyed to Frankfort by three small wires of 

 No. 8 gauge, which may be roughly described as about the size of 

 the stem of a clay tobacco pipe. At Frankfort the current is 



