SOLAR RADIATION AND ATMOSPHERE — STETSON 153 



quencies produce their own special effects upon the earth and its 

 atmosphere. 



We are all familiar with the fact that if sunlight is split into 

 its component colors by means of a spectroscope we can see a large 

 variety of the radiations represented by the various parts or colors of 

 the solar spectrum. The visible range to which the eye responds 

 represents frequencies extending from 400 million million cycles per 

 second to a frequency just about double this, or 800 million million 

 cycles per second. The sensation of the higher of these two frequen- 

 cies is that of violet light, and the sensation produced by the 400 mil- 

 lion million cycle frequency is that of deep red light. In between these 

 two extremes of the spectrum fall the intervening colors. But outside 

 this so-called visible range to which the eye responds there is a vast 

 scale of radiations both beyond the red end of the spectrum, which 

 we call the infrared, and far down below the violet, which we call 

 the ultraviolet. 



By means of the photographic plate, we can extend the map of 

 the spectrum in either direction. Far out beyond the red end are 

 heat radiations from the sun that may be measured with the thermo- 

 pile or the bolometer. Today much research is being done in measur- 

 ing the extremely short waves, or high-frequency radiations out beyond 

 the violet, for the ultraviolet is coming to have increasing importance 

 not only from the point of view of health but from the point of view 

 of the radio engineer. 



The sunlight which we measure or analyze at the earth's surface 

 is, however, seriously modified by the absorption introduced by the 

 constituents of our own atmosphere. As we all know, the earth's 

 atmosphere consists of nearly 14 oxygen and % nitrogen. There is a 

 sprinkling of carbon dioxide with a bit of argon, neon, crypton, xenon, 

 and a trace of helium. Here at the earth's surface we can count on a 

 little more than 1 percent of water vapor. For a thorough mixing 

 of the elements of this atmosphere and the maintenance of its tempera- 

 ture as well as the variation in its temperature, we rely upon the sun. 

 Occasionally we have vividly impressed upon us the relationship of 

 our atmosphere to disturbances on the sun, by displays of aurorae or 

 the Polar Lights, often flaming gorgeously red and stretching 100 

 miles above the earth. These glowing electric discharges advertise 

 the lofty air swarming with the traffic of electrons, ions, and particles, 

 jostling one another as they are excited by radiations from the sun 

 peculiar to the occurrences of sunspot activity. 



Observations with the spectroscope indicate that there is much 

 radiation at the extreme ultraviolet end of the spectrum to which 

 the earth's atmosphere is completely opaque. A great deal of the 

 absorption of this region of the solar spectrum of very short wave 

 lengths is caused by a layer of ozone which exists at an average height 



