U'lI.I.JAM SIEMENS, F.R.S 195 



By this arrangement of furnace great economy is attained, great 

 cleanliness of working and purity of flame ; but it has been prin- 

 cipally valuable, as owing to the great heat obtainable, it has 

 enabled metallurgical processes to be effected, which cannot be 

 attempted in ordinary furnaces. The temperature is limited 

 theoretically by the point of dissociation (or the point at which 

 the energy of chemical affinity is overcome by that of sensible 

 heat ), and practically by the resistance to fusion offered by the 

 refractory materials employed in the construction of the furnace. 

 The economy is proved by the fact that a ton of iron can be heated 

 to the welding point with 7 cwts. of coal ; and a ton of steel 

 melted with 12 cwts., whilst from 2 to 8 tons of coke were formerly 

 employed to produce the same effect. 



Having thus dealt with the two principal applications of coal 

 to useful purposes, I pass over its manifold other applications for 

 domestic and general uses, and ask you to accompany me to the 

 consideration of that other great store of energy, the tidal wave. 

 In order to utilise this, large basins or reservoirs would have to be 

 provided along the shore of the tidal sea or estuary, to be filled 

 with tidal water during the flood, and to be discharged during the 

 ebb of the tide. The energy of the inflowing and outflowing 

 stream of water can best be utilised by means of such turbine or 

 vortex-wheel as we owe to Professor James Thomson, and is a 

 matter with which I need not detain you at present. What I wish 

 to show is, what is the amount of power recoverable with a given 

 area of tidal basin, and a given rise or fall of tide. 



Suppose the actual rise of tide to be 12 feet, 8 feet would be 

 available during half the time of the rise or fall, which would 

 be equivalent to an effective head of 4 feet during the twenty 

 hours, what is the power that can be utilised per acre of surface ': 

 An acre of ground contains 43,560 square feet, and the weight of 

 sea water is 64 Ibs. per cubic foot ; multiplying these numbers 

 into the height of fall, and dividing by the equivalent of 1 horse- 

 power, we obtain V6 horse-power as the effective energy of an acre 

 of impounded sea water. Considering the great cost of construct- 

 ing sea walls to form these tidal basins, and considering also the 

 value of the foreshores in estuaries, or protected portions of the 

 seashore, where alone such constructions would be practicable, it 

 will be at once apparent that the utilisation of the tidal wave is 



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