THE SUN AND THE ATMOSPHERE — STETSON 151 



If we live where we obtain our electric current from utility com- 

 panies operating solely by water power, we do not dodge the issue of 

 our debt to the Solar Power Company. The radiation from the sun 

 transforms the water of the oceans, lakes, and streams into the 

 ascending water vapor that condenses into clouds and falls in rain, 

 feeding mountain streams, and rivers that turn the giant turbines 

 of the hydroelectric plants. A fair estimate of the amount of water 

 evaporated and precipitated in rainfall in 1 year is 480 million million 

 tons. To carry on this gigantic irrigation enterprise requires the 

 expenditure of 1,000 million horsepower continuously throughout 

 the year, yet only a very small amount of solar energy is consumed 

 in running this rain-making machinery. 



How long the Solar Power Company can continue to operate 

 depends upon its source of supply, and to answer this question we 

 must avail ourselves of the best guesses of science. Dismissing as 

 utterly inadequate earlier hypotheses, our best guess now is that the 

 chief source of energy is within the atoms of which the sun is composed. 

 The two simplest atoms about which we know anything are those of 

 hydrogen and helium. Hydrogen is the highly explosive gas which 

 was the cause of the Hindenburg disaster, and helium is the inert 

 nonexplosive gas which those responsible for this giant airliner would 

 have liked to have substituted for hydrogen, could they have obtained 

 it. Four hydrogen atoms constitute the necessary building material 

 for one helium atom with just a bit of energj 7 left over. 



It appears probable that within the hot interior of the sun the trans- 

 mutation of hydrogen into helium is continually taking place, thus 

 releasing an enormous amount of heat from the surplus energy left 

 over from each combination of four hydrogen atoms as they form one 

 helium atom. Every time such a transmutation takes place one per- 

 cent of the weight of the materials involved is liberated as energy. 

 On such an hypothesis the sun could have well kept up its present 

 state of radiation from as far back in geologic time as we have any 

 reason to consider. Of course the sun is constantly losing weight in 

 the process. The loss of weight has been calculated to be 4,200,000 

 tons every second, but we scarcely need worry about the fuel supply 

 being exhausted while the sun still has about 2,000,000,000,000,000,- 

 000,000,000,000 tons of matter left in it! 



Passing over reminders of our indebtedness for the various services 

 the sun renders, we shall come to see that we are quite as much 

 interested in analyzing the kinds of radiation that the sun sends out 

 as we are in the total amount of energy received. When we analyze 

 this radiation we discover that it covers a wide range of frequencies 

 or wave lengths. It seems probable that each of these wave lengths 

 or frequencies renders a special kind of service to the earth and its 

 atmosphere. 



