6 OUR PHYSICAL WORLD 



Storms are perpetually raging and the furious movements of 

 the heated gases are seen even at our great distance. Sometimes 

 the down draft of the cooler outer portions appears to pour 

 through rifts in the gas mantle so swiftly as to cool off the fiery 

 interior a bit, and then the throat of the cyclonic movement 

 seems dark as seen against the brilliant deeper portions, and we 



FIG. 2. Sun spots. Photograph by Miss Mary Calvert, taken with the 

 12-inch telescope at Yerkes Observatory, August 7, 1917. 



designate the object a sun spot (Fig. 2). Such spots are some- 

 times many thousands of miles in diameter, large enough to 

 be seen through a smoked glass by the naked eye. They are of 

 great interest since by watching them it was determined that the 

 sun rotates on its axis from west to east once in about twenty-five 

 days, a fact confirmed by other methods of observation. Their 



