20 The Outline of Science 



The actual temperature at the sun's surface, or what appears 

 to us to he the surface the photosphere is, of course, unknown, 

 hut careful calculation suggests that it is from 5,000 C. to 7,000 C 

 C, The interior is vastly hotter. We can form no conception of 

 Midi temperatures as must exist there. Not even the most ob- 

 durate solid could resist such temperatures, but would be con- 

 verted almost instantaneously into gas. But it would not be gas 

 as we know gases on the earth. The enormous pressures that 

 st on the sun must convert even gases into thick treacly fluids. 

 We can only infer this state of matter. It is beyond our power 

 produce it. 



Sun-spots 



It is in the brilliant photosphere that the dark areas known 

 as sun-spots appear. Some of these dark spots they are dark 

 only by contrast with the photosphere surrounding them are of 

 enormous size, covering many thousands of square miles of sur- 

 face. What they are we cannot positively say. They look like 

 great cavities in the sun's surface. Some think they are giant 

 whirlpools. Certainly they seem to be great whirling streams 

 of glowing gases with vapours above them and immense upward 

 and downward currents within them. Round the edges of the 

 sun-spots rise great tongues of flame. 



iaps the most popularly known fact about sun-spots is 

 that they are somehow connected with what we call magnetic 

 storms on earth. These magnetic storms manifest themselves in 

 interruptions of our telegraphic and telephonic communications, 

 in violent disturbances of the mariner's compass, and in excep- 

 tional auroral displays. The connection between the two sets of 

 phenomena cannot be doubted, even although at times there may 

 be a great spot on the sun without any corresponding "magnetic 

 storm" cll'ccts on the earth. 



A surprising fact about sun-spots is that they show definite 

 periodir variations in number. The best-defined period is one of 



