124 Trans. Acad. Sci. of St. Louis. 



Correction. — In Vol. XXII, No. 2, p. 59, line 1 from 

 the top, erase the before Ampere. 



EXPLANATION OP THE PLATES. 



Plate XXI. — A local magnetic storm due to a local gust of wind of 

 very unusual severity, lasting ten minutes, on a calm day. The wind 

 storm reached the station nine minutes after the magnetic disturbance 

 began, the time being indicated by the arrow. 



Plate XXII. — A local magnetic storm due to a violent and very local 

 fall of rain. 



Plate XXIII. — A decrease in the horizontal intensity of the earth's 

 magnetic field, due to two dense clouds surrounded by clear sky, pass- 

 ing over the sun, shown on the diagram at 11 a. m. and 4:30 p. m. 



Plate XXIV. — A magnetic storm such as was observed usually on 

 clear days shortly before sunset. 



Issued October S, 1918. 



