4 ELECTRIC LIGHTING. 



sufficed to convince him that the problem might one day be 

 solved, and this, in fact, is what we now see. In order, 

 however, to arrive at a result so important as that which we 

 have stated, Clamond had to devote himself to a great 

 number of experiments and numerous investigations, and it 

 was only after nine years had passed that he was able to 

 solve the problem completely. One of Clamond's piles, 

 arranged nearly like a heating apparatus, and having its 

 dimensions not greater than 1-50 metres in height and 80 

 centimetres wide, is now able to supply three electric lamps, 

 each equal to from 15 to 20 gas-burners, and requiring for the 

 whole expense of the supply of electricity, the burning of 

 only 9-5 kilogrammes of coke per hour. It will be seen that 

 this is a considerable result, and the more important since 

 an apparatus of this kind does not require the attention of a 

 mechanic or skilled workman. The apparatus may be placed 

 in a cellar and so arranged that it may be used as a heating 

 apparatus, and any person is able to work it, since it. needs 

 only to be heated like an ordinary stove. 



But let us state on what principle this ingenious apparatus 

 is founded. 



If pieces of two different metals are soldered together by 

 one end of each, and the soldered portion be heated, the 

 movement of the heat takes place differently in the two 

 metals, and gives rise to an electro-motive force which supplies 

 an electric current that may be collected from the free ex- 

 tremities of the metals. The simple metals, the junction of 

 which affords the most marked thermo-electric effects, are 

 bismuth and antimony ; but, as we have already said, alloys 

 and certain metallic minerals give effects much more power- 

 ful. At first Clamond's pile was made of bars of galena 

 soldered to plates of sheet-iron ; but he soon had to abandon 

 the use of galena, and he resorted to an alloy composed of 

 antimony and zinc, while still retaining sheet-iron as the 

 electro-positive plate. By arranging these elements in a 

 ring, placing several of these rings one above the other, 



