196 



however, it mattered little that the output of steam was about 

 17 per cent, greater at mid-day than in the morning and 

 evening. 



The maximum thermal efficiency of the Egyptian sun-heated 

 boiler was 40*7 per cent., which compared very favourably with 

 the thermal efficiency of an ordinary steam boiler of about 

 70 per cent., when the relative state of development of the two 

 types of boilers was taken into account. 



During the discussion of a paper on " The Utilization of 

 Solar Energy," which I read before The Society of Engineers 

 (Incorporated) last April, a speaker pointed out that glass 

 mirrors cause a loss on account of the absorption of the radiant 

 energy by the glass of the mirrors. This is true, and. possibly 

 the loss may amount to 15 per cent., but it is important to 

 remember that when solar radiation had been passed through 

 one sheet of glass, the rays which emerge are more capable 

 of passing through a second sheet of glass. In other words, 

 practically all those which could not pass through glass were 

 stopped by the first sheet, so that when the radiation was 

 reflected from the silvered surface of the glass back through 

 the latter, a second 15 per cent, was not lost. Metal reflectors 

 would much reduce the loss by absorption 'compared with the 

 silvered glass reflectors and would no doubt be more efficient, 

 but unfortunately no practical metal reflector could be used 

 which would have a sufficiently 'hard and untarnishable surface. 

 If the surface were not hard it would get scratched by repeated 

 removal of dust, and if it were not untarnishable it would also 

 lose its efficiency. 



The PRESIDENT : Mr. Chairman and Gentlemen I am afraid 

 I can only make a small contribution to the discussion. I have 

 followed the results of this scheme of Mr. Shuman's with 

 much interest, and a short time ago I went to Meadi, in Egypt, 

 in order to see the plant at work. I regret, however, to say 

 that on this occasion the sun had not been seen for a week, and 

 the Nile 'had fallen far below the intake for the water. I was 

 therefore obliged to come away without seeing the plant in 

 operation. At the same time, I feel that the attempts Mr. 

 Shuman is making are not only most interesting and important, 

 but are certainly attempts which ought to be systematically 

 continued, because it looks, especially from what Mr. Acker- 

 mann has just told us of the thermal efficiency, that provided all 

 mechanical difficulties can be got over, we shall be in possession 

 of a source of power for the tropics which will be extremely 

 efficient and extremely economical. I hope that before the 

 Congress meets again we shall have a further report showing 

 that success has been met with in more than one place. 

 One difficulty which occurs to me is that the actual amount of 



