458 MAGNETIC VAEIATION. t 



The needle also varies very considerably at times in the course of the 

 day, this diurnal change amounting to 7', 8', 9', and 10'; the maximum 

 "Westerly Declination is at 2 p.m. This topic is so large and comprehen- 

 sive, that if further information be required beyond that given here, and 

 in the Section on Magnetism and the Compass at the end of this work, 

 reference must be made to other works devoted entirely to the subject. . 



(471.) Magnetic Storms. — The daily oscillation in the Variation, or 

 magnetic declination, of the Compass, is too small, even in so-called 

 " Magnetic Storms," to be of any importance in practical navigation. 



From the 13th to the 18th of May, 1891, a Magnetic Storm was observed 

 at the Naval Observatory, Washington, U.S., during which the needle 

 varied 48' in direction in 9^ hours, the North end being drawn 35' to the 

 Eastward of its normal direction. 



During another such storm, February 13th to 14th, 1892, at the same 

 Observatory, the needle oscillated on each side of the mean position, 

 registering a change of direction of 1° towards the East, and nearly 30' 

 towards the West. This unusually severe Magnetic Storm is of especial 

 interest, as it occurred at the time of the appearance of a large group of 

 sun-spots, and of fine displays of aurora. 



