192 
day or longer, depending upon the latitude in which they are 
placed. : 
The Cairo plant gave sufficient steam to produce 50 b.h.p. for 
ten hours per day, and had it been located further south it 
would have given probably 65 b.h.p. 
The absorbers are constructed to withstand all the wind of 
the tropics, whilst the mirrors are set in spring frames so as 
to avoid any risk of breakage and can be cleaned by washing 
with a hose. The power generated by the rays of the sun can 
be stored so as to keep up the supply of power during the 
whole of a rainy day or through the night by means of storing 
heat in boiling water, and the engine has been designed to 
work economically on this system, which is in extensive use 
in America. 
Sun-power plants occupy a large area, but in places where 
they will be installed in the tropics land is very cheap indeed, 
and the ground rent of a sun-power plant will be only a fraction 
of that of a plant of equivalent size in any of the manufacturing 
centres of Britain. ; 
All the materials used in the construction of this plant are 
of the simplest kind, and therefore the cost of upkeep is very 
slight. 
There is a large field all over the tropics for sun-power plants 
where fuel prices are high and where land at present is not 
irrigated owing to the excessive cost of fuel and the absence 
of surface water. Sun-power plants could be built to meet 
the immediate requirements, and then be added to as the 
population increases. In this way there will be an enormous 
saving. 
Sun power, of course, is independent of any combination of 
capital or labour. Every year coal and oil become more 
expensive, and as time goes on it will, therefore, be better and 
better for sun power. 
An area of 143 square miles in the Sahara Desert covered 
with sun-power plants would furnish as much power as that 
produced by the whole of the coal and oil supply of the world, 
and as much heat as would be produced by the combustion 
of our entire store of coal and oil is thrown to the earth by 
the sun in three years. 
The lecture was illustrated by means of a cinematograph 
film showing the plant at Cairo at work. 
[ Discusston. ] 
The Cuatrman: Gentlemen—Of all the large number of 
admirable papers delivered at this Congress within the last 
three days, I am sure none has attracted greater attention and 
