204 AISTNUAL REPORT SMITHSONIAN INSTITUTION, 1942 



FiGtTRE 14. — Records of magnetic storm (A) September 17-18, 1941, and (B) 

 September 18-19, 1941, Cheltenham Magnetic Observatory, Maryland. (Cour 

 tesy of U. S. Coast and Geodetic Survey.) 



The coronal display was visible simultaneously in widely separated parts of 

 the country. To all observers everywhere the rays seemed to converge toward a 

 point slightly south of the zenith. Actually, of course, there was no con- 

 vergence. The particles shot off from the Sun, being electrically charged, can 

 not freely cross the Earth's magnetic field and must travel in the direction of 

 the magnetic lines of force. At Washington, the lines of force are tilted about 

 20° southward from the vertical while farther north the tilt is less. Thus all 

 observers were viewing a bundle of closely parallel rays, extending tens or 

 hundreds of miles upward in the rarefied atmosphere, and appearing to con- 



