rays has only been solved after seven years of patient experi- 

 mental work and the expenditure of very large sums of 

 money. 



An experimental plant was erected at Cairo in Egypt, this 

 position being chosen on account of its convenience, as it was 

 desired to use the plant for demonstration purposes. As the 

 fuel cost absolutely nothing, the question of mechanical 

 efficiency did not require to be taken into account. It was a 

 question altogether of construction, upkeep and labour; and 

 if the interest on the capital added to the cost of upkeep and 

 attendance was so high as to cancel the profit made by not 

 requiring fuel, then there was no incentive to go further in 

 the matter. 



However, the results of tests of the plant had been very 

 satisfactory, and it was estimated that power could be produced 

 in the tropics at the same cost as if coal were less than IDS. per 

 ton, and as coal in many parts of the tropics costs 2 los. 

 per ton and upwards, the saving to be effected by means of 

 sun-power plants is quite obvious. Although sun-power plants 

 cost more than coal-burning plants, the saving effected 

 by not requiring any fuel is sufficient to wipe out the extra 

 capital cost after two years, and to pay entirely for the plant 

 in four years. 



The steam produced from the rays of the sun is exactly the 

 same as that obtained from the burning of any fuel, and there- 

 fore the power can be used for any purpose whatever. The 

 engine is a low-pressure reciprocating condensing engine, and 

 the pump an ordinary reciprocating pump. Experience has 

 shown that steam at atmospheric pressure gives the greatest 

 return in power per pound sterling invested, and therefore the 

 engine runs on steam supplied at this pressure. The steam is 

 generated in five absorbers 13 ft. wide and 200 ft. long, which 

 are parabolic troughs for catching the sun's rays on mirrors 

 and throwing the rays on to a boiler swung at the focal point. 

 The rays are absorbed by the black surface of the boiler, and 

 the heat is sufficient to generate large quantities of steam. The 

 absorbers are placed with sufficient clearance so that they do 

 not shade each other in the morning and evening. They rotate 

 on a system of gearing in such a manner that the mirrors 

 point directly towards the sun at all times of the day, and the 

 correct adjustment is effected by means of a thermostat 

 operated by the sun itself. The steel framework of the 

 absorbers is designed in such a manner that it can be manu- 

 factured very cheaply, and as each piece is very light, the 

 question of transportation is not a serious one. 



Sun-power plants in this system can be built of any size up 

 to 10,000 h.p. if required, and will work for ten hours per 



