THE SUN AND THE ATMOSPHERE STETSON 159 



discovery of the magnetic character of sunspots themselves by Dr. 

 Hale and the more recent discovery of an ionized region in the upper 

 atmosphere of the earth that any real explanation appeared as to why 

 sunspots and changes in the earth's magnetic field should show so 

 close a parallelism. 



Everyone knows in a general way that the earth is a magnetic 

 sphere. That the compass needle does not point true north except in 

 various restricted parts of the globe is also a fact which is generally 

 recognized. Perhaps comparatively few people realize, however, that 

 the compass needle is constantly wandering back and forth every day 

 by a slight amount. When the sun rises in the east, the north end of 

 the compass needle turns slightly toward that direction. By noon 

 when the sun is south, it is pointed in its normal position. Then in 

 the afternoon as the sun wanders and sets in the west, the compass 

 needle wanders likewise to the west, coming back again to its normal 

 position about midnight when the sun is below the northern horizon. 

 This goes on day after day, month after month — but during the years 

 when sunspots are most numerous these daily excursions of the com- 

 pass needle will on the average be twice as great as during the years 

 when sunspots are lacking. These diurnal wanderings of the compass 

 needle can now be roughly explained as due to the effects of ionization 

 of the upper atmosphere by sunlight. As the electric charges become 

 separated in the process of ionization of the molecules of nitrogen and 

 oxygen under the bombardment of ultraviolet light from the sun, the 

 movements of these ions create a perceptible current, deflecting the 

 compass needle from its normal magnetic position. We may infer, 

 therefore, that at times of sunspot maxima the number of these ions 

 in the upper air is materially increased, producing a more marked 

 magnetic effect. The strength of the magnetic field of the earth, there- 

 fore, may be considered as increasing and decreasing with the variation 

 in the intensity of the ionization of the upper air that changes with 

 sunspot occurrences. Most of our knowledge of the ionized region 

 has come about through the invention of radio. 



In the early days of wireless, it was thought that electric waves 

 which carried telegraph messages without wires traveled in straight 

 lines over the earth, just as light waves do. With this conception one 

 could never hope to communicate over very great distances, since the 

 curvature of the earth would prevent the passage of the waves as the 

 earth's huge hulk bulged into the communication path. The earlier 

 wireless engineers thought that only by building higher and higher 

 antenna towers could one ultimately hope to communicate over the 

 thousands of miles that would make transoceanic wireless possible. 



How amusing such a picture appears when today any one of us can 

 turn the knob on our short-wave sets and bring in broadcasts from 

 London, Rome, or Berlin. Of course, these early crude notions about 



