152 ANNUAL REPORT SMITHSONIAN INSTITUTION,, 1942 



lower regions in which our weather appears to arise. All weather is 

 fundamentally traceable to solar radiation. The amount and the char- 

 acter of this radiation, particularly in its relationship to atmospheric 

 phenomena, merits more detailed consideration. 



From observations at the Smithsonian Institution, the amount of 

 energy that the sun emits has been measured with such precision that 

 we know not only the quantity of heat and light emitted, but that this 

 quantity varies from time to time by some 2 or 3 percent. The aver- 

 age energy received by the earth from the sun is about 450 million 

 million horsepower. Because of the relatively insignificant size of the 

 earth, and also the great distance that separates us from the sun — 

 a distance of 93 million miles — our planet can intercept but about 

 one two-billionth of the total solar output. Even so, if we stop to 

 consider what the cost to us would be were we charged for a year's 

 service of heat and light from the Solar Utilities Power and Liglit 

 Company, we would find our indebtedness mounting to staggering pro- 

 portions. At a price of 1% cents per kilowatt hour, the annual budget 

 that would have to be allowed for sunshine for the continental United 

 States alone would represent an expenditure of 327 quadrillion dollars. 

 Such figures are indeed difficult to imagine. If we change our picture 

 to a more restricted one, we can say that the cost of sunshine for Greater 

 New York at the above figure would amount to approximately 100 

 million dollars for the average day. Fortunately for us, millions of 

 years ago this same sunshine provided the energy for growing the 

 vast tropical forests of the carboniferous era. The carbon in those 

 fallen tree trunks that we are mining today in the form of coal together 

 with the water power provided by the vast irrigating systems main- 

 tained by the sun's radiation is the source for the maintenance of our 

 public utilities and industries today. It is an interesting question as 

 to how long the sun can maintain its present output of radiation and 

 how far into the future we may rely upon its ability to furnish us with 

 this all-essential source of energy. It appears probable that within 

 the hot interior of the sun, which may be estimated in terms of millions 

 of degrees, an atomic transmutation is taking place that has been going 

 on for millions of years and is likely to continue for a long time to 

 come. Through an ingenious carbon cycle recently worked out by 

 Professor Bethe, of Cornell University, we picture the ultimate trans- 

 formation of hydrogen into helium with the continual release of 

 energy in the form of radiation that represents a loss of mass to the sun 

 of some 4,200,000 tons every second. We scarcely need worry, how- 

 ever, about the deterioration of the fuel supply while the sun has about 

 2,000,000,000,000,000,000,000,000,000 tons of matter still left in it. 



If we analyze the radiation from the sun we discover that it covers 

 a wide range of wave lengths. Certain of these wave lengths or fre- 



