222 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1952 



that can be a competitor of the sun. It is fortunate that we shall 

 continue to have plenty of solar energy, which, directly or indirectly, 

 serves to keep the world an attractive place in which to live. 



Of the annual land vegetation, only 14 percent is consumed as 

 food, fuel, lumber, paper, and chemicals. The balance of 86 percent 

 is returned to the earth to maintain essential biological balance. With 

 our ever-increasing population, it is doubtful whether the fuel use 

 of vegetation can be increased to any very great extent. 



Sooner or later the inexhaustible supply of energy from the sun 

 will be used to supplement, or in large measure to replace, energy- 

 containing materials on earth. Only limited progress has so far 

 been made. Of the scientists' approaches for collecting the sun's 

 energy several have shown some promise. A popular study has been 

 that of the single-celled alga Ghlorella pyrenoidosa. This plant mul- 

 tiplies at a rate that appears to be limited only by the carbon dioxide 

 content of the water. Carbon dioxide in the air amounts to 0.03 

 percent. It has been found that algae in pans of water 6 inches deep 

 are capable of absorbing up to 2 percent of the total solar energy 

 falling on a given area as compared with less than 0.1 percent for 

 average agriculture. A yield of 15 dry tons per acre has been 

 realized, which is nearly five times that of the best land growth, 

 and scientists believe that this yield can be trebled. The Carnegie 

 Institution has recently reported what is claimed to be the first large- 

 scale experiments with Chlorella. Whether these algae may be used 

 directly for cattle or human food, or whether they may be converted 

 more profitably into chemicals or fuel is a problem for the future. 

 To provide 1 billion barrels of motor fuel from algae would require 

 an area of 35,000 square miles, assuming 35 dry tons of algae per acre 

 could be obtained. 



Photosynthesis, the process by which all vegetation is created, is 

 not well understood. In essence, the plant converts the low-energy 

 compounds, carbon dioxide and water, to carbohydrates and oxygen 

 in the presence of chlorophyll. Attempts have been made to replace 

 chlorophyll by synthetic dyes and inorganic chemicals. It has been 

 reported that from certain experiments an amount of energy is ab- 

 sorbed equivalent to that absorbed in the presence of chlorophyll. 



The use of glass, sometimes with reflectors, to collect the heat from 

 the sun shows promise of becoming practical. Energy absorption 

 seven times as efficient as the most optimistic agricultural proposals 

 has been claimed. Apparatus is now in use for the heating of water 

 by the sun. 



Phosphors are chemicals that absorb radiant energy and radiate it 

 after a certain length of time. Such chemicals might be employed to 

 absorb energy from the sun during the day and for illuminating pur- 



