218 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



note that the atmosphere above the clouds tends to be smooth. No 

 more balloons or thermals. No more "convection," as we term the 

 rising and falling of air. The "balloons" have reached a ceiling where 

 the air above is quiet and stable. 



I ask you to bear with me a moment longer, while I discuss the 

 horizontal flow of air masses. The sun heats the earth's atmosphere, 

 as the earth turns on its axis, like a roast on a spit. The heating is 

 greatest near the equator and the gas will rise in that area, allowing 

 the cooler air from the poles to flow in and take its place. The phe- 

 nomena of weather and atmospheric circulation are very complex. 

 But the basic flow comes from absorbed solar heat, with forces of the 

 earth's rotation playing an important part. 



And so, in the vast sea of air, we find not only violent streams of 

 vertical turbulence, but also streams and patterns of horizontal flow. 

 These include tornadoes and hurricanes and the over-all pattern of 

 cyclonic weather. 



But what has this sea of terrestrial air to do with the solar 

 atmosphere ? Ever since man started to observe the sun, astronomers 

 have employed analogy with the earth's atmosphere as a means of 

 interpreting solar phenomena. Galileo himself, discoverer of sun- 

 spots, suggested that the dark areas were clouds of a sort, floating in 

 the sun's atmosphere and carried across the disk by simple rotation. 

 In this view, elementary as it was, Galileo was far nearer the truth 

 than were many of his successors. He at least recognized the atmos- 

 pheric nature of the phenomena. Lalande, for example, suggested 

 that spots were cold mountain peaks, towering above the luminous 

 surface. And even the great William Herschel, again influenced by 

 analogy and his preconceptions, regarded spots as holes in the fiery, 

 luminous clouds, through which we could glimpse the cool surface 

 beneath. 



In 1794 Herschel wrote : 



The sun . . . appears to be nothing else than a very eminent, large, and lurid 

 planet, evidently the first or, in strictness of speaking, the only primary one of 

 our system ; all others being secondary to it. Its similarity to the other globes 

 of the solar system with regard to its solidity, its atmosphere, and its diversified 

 surface; the rotation upon its axis, and the fall of heavy bodies, lead us on to 

 suppose that it is also most probably inhabited, like the rest of the planets, by 

 beings whose organs are adapted to the peculiar circumstances of that vast globe. 



Peculiar indeed, in the light of modern knowledge! Even in the 

 relatively cool solar atmosphere, the temperature is so high that all 

 chemical substances are vaporized. 



But even if Herschel proposed a view that we cannot accept today, 

 he did recognize the importance of circulation in maintaining the 

 physical state of the solar atmosphere. His theory was not idle specu- 

 lation. He visualized the presence of violent winds and suggested 



