PRESIDliNTFAL ADDRHSS — SECTION A. 



27 



the pmvcr su]i]il\ . ll is not likcl_\ that a solar entwine would be avail- 

 able for more than ).? of the day, or, say, 3.000 hours ])er annum. 

 This disadvantaoe has been elearly realised by solar entwine 

 inventors, who have included, amongst otiicr contrivances to 

 obviate it. a conil)ination of a windmill for use in cloudy weather, 

 compressed air tanks, electrical storage batteries, and water 

 pumped into a highl\- elevated reservoir and then used to drive a 

 water turbine. 



If engineers mav be sceptical. Sluuuan. the inventor, is 

 undoubtedly optimistic. Starting with the statement fre(|uently 

 quoted, that all the coal mined in the world is e(|uivalent to 

 270,000.000 h.p. continuously throughout the \-ear, and assuming 

 that his Cairo plant developes 50 h.]). during a lo-hours day. and 

 that it occupies less than i acre, and that it intercepts 13.270 sq. 



Fig. 5. — Sugsestion for utilising a sun-backed roof for solar engine for 



heating purposes. 



feet, or less than ^ acre of sunlight, he proceeds to unfold a 

 wonderful scheme of power production. He calculates that it 

 would only be necessary to cover 20,250 sq. miles, or a square of 

 143 miles side, of ground in the Sahara desert with sun-heat 

 absorber units, spaced as wide apart as they are at Cairo, to give 

 perpetually the 270 million h.p. per year to equal all the coal 

 mined in 1909. Fig. 4 shows to scale the space occupied In this 

 ])ower-i)lant on the map of Africa. 



" Stu'ely." he says, " from this showing, the htiman race can 

 see that sun-power can take care of them for all time to come." 

 The cost of this truly American scheme he estimates at £19.700 

 millions sterling. " But," he continues, '' this vast investment 

 Avould not be made for or by the individual, but for and by the 

 entire httman race, and we can safely assume the human race to 

 survive all the coal and oil fields by many thousands of xears. 



