266 UTILIZING THE SUn's ENERGY. 



of power thus derivable from the direct rays of the sun. His appa- 

 ratus was simple — merel}^ a conical mirror or reflector, receiving 

 the heat of the sun on as large an area as was desired and was found 

 practicable, and directing it to a focus where was placed a steam boiler 

 or an air cylinder within which the fluid, heated to a high temperature, 

 became available for use in a steam or an air engine. He reported the 

 results of his experiments thus: * 



"It has already been stated that the result of repeated experiments 

 with the concentration apparatus shows that it abstracts on an average, 

 during nine hours a day, for all latitudes between the equator and 

 45°, fully 3.5 units of heat per minute for each square foot of area 

 presented perpendicularly to the sun's rays. Theoretically this indi- 

 cates the development of an energy equal to 8.2 horsepower for an 

 area of 100 square feet. On grounds before explained, our calcula- 

 tions of the capabilities of sun power to actuate machinery will, how- 

 ever, be based on 1 horsepower developed for 100 square feet exposed 

 to solar radiation. The isolated districts of the earth's surface sufi'er- 

 ing from an excess of solar heat being very numerous, our space only 

 admits of a glance at the sun-burnt continents, 



"There is a rainless region extending from the northwest coast of 

 Africa to Mongolia, 9,000 miles in length and nearly 1,000 miles wide. 

 Besides the north African deserts, this region includes the southern 

 coast of the Mediterranean, east of the Gulf of Cabes, Upper Egypt, 

 the eastern and part of the western coast of the Red Sea, part of Syria, 

 the eastern part of the countries watered by the Euphrates and Tigris, 

 eastern Arabia, the greater part of Persia, the extreme western part 

 of China, Thibet, and, lastl}^, Mongolia. In the Western Hemisphere, 

 Lower California, the table-land of Mexico and Guatemala, and the west 

 coast of South America, for a distance of more than 2,000 miles, sufi'er 

 from continuous intense radiant heat. 



"Computations of the solar energy wasted on the vast areas thus 

 specified would present an inconceivably great amount of dynamic 

 force. Let us, therefore, merel}' estimate the mechanical power that 

 would result from utilizing the solar heat on a strip of land a single 

 mile in width along the rainless western coast of America, the south- 

 ern coast of the Mediterranean, before alluded to; both sides of the 

 alluvial plain of the Nile in Upper Egypt, both sides of the Euphrates 

 and Tigris for a distance of 400 miles above the Persian Gulf, and, 

 finally, a strip, 1 mile wide, along the rainless portions of the shores 

 of the Red Sea, before pointed out. The aggregate length of these 

 strips of land, selected on account of being accessible by water com- 

 munication, far exceeds 8,000 miles. Adopting the stated length and a 

 width of 1 mile as a basis of computation, it will be seen that this 

 very narrow belt covers 223,000,000,000 square feet. Dividing the 

 latter amount by the area of 100 square feet necessar}^ to produce 1 

 horsepower, we learn that 22,300,000 solar engines, each of 100 horse- 

 power, could be kept in constant operation nine hours a day by utiliz- 

 ing only that heat which is now wasted on the assumed small fraction 

 of land extending along some of the water fronts of the sun-burnt 

 regions of the earth. 



* Contributions to the Centennial Exhibition, by John Ericsscn, 1876. D. Van 

 Nostrand, New York. 



