408 MISCELLANEOUS SUBJECTS 



an average of 50 b.h.p. This same plant, if set up 1,000 

 miles further south would probably give 65 b.h.p. 



The steam produced was practically at atmospheric 

 pressure, although the engine would work well with 

 steam at considerably lower pressures. For instance, if 

 a cloud passes over the sun for, say, ten minutes, then 

 the engine draws on the reserve of steam held in the 

 boiling water contained in the boiler, and will lower the 

 pressure down to 4 Ib. absolute before it would come to 

 a stop. Early in the morning and late in the afternoon 

 the engine also runs at pressures below the atmosphere, 

 giving a corresponding amount of power. 



The boilers of the present plant are surrounded by a 

 single thickness of thin window-glass for the purpose of 

 cutting down the losses by conduction and convection, 

 particularly when the wind is blowing strongly. 



The heaters are so constructed that they will stand a 

 wind pressure of 30 Ib. to the square foot safely. This 

 means that they are entirely proof against any of the 

 ordinary gales which may obtain in the tropics. 



All the mirrors and glasses used in the construction 

 of these heat absorbers are held in place by means of 

 small brass springs in a very flexible manner, which pre- 

 vents breakage due to expansion and contraction, and also 

 means resilience to hail. In the regions where the sun- 

 power plants are proposed, hailstorms are practically 

 unknown, but at the same time this method of setting 

 them means that they will stand considerably more hail 

 than the ordinary hot-houses in which the glass is set 

 rigidly. 



It will, of course, be asked: What will 'be the effect 

 of dust settling on the mirrors and on the glass? Any 

 dust settling on the mirrors and the glass, of course, 

 means loss of power, according to the thickness of the 

 dust. Therefore we must keep our mirrors clean. 

 Labour is veiy cheap in the tropics, and 20 pence a day 

 to do this work would be sufficient to keep the mirrors 

 entirely clean, the proper washing arrangements, of 

 course, being provided. 



Resolved to its first principles " sun-power " is a very 

 simple proposition. Provide a boiler, throw plenty of 

 sun's rays upon it, and generate your steam. To make 



