1!»10] on Magnetic Storms. 



Table II. — Absolute Ranges of Declination. 



775 



As already explained, the forces required to displace the needle 1 ' 

 out of the magnetic meridian at Kew and 3' out of the magnetic 

 meridian at the Antarctic station are approximately equal. If then 

 the disturbing forces at the two places were of similar magnitude, 

 we should expect ranges under 30' in the Antarctic to be as common 

 as ranges under 10' at Kew, and on the other hand ranges over 40 

 at Kew to be as common as ranges over 120' in the Antarctic. This, 

 it will be seen, is exceedingly wide of the mark, ranges over 120' 

 being 39 times as common in the Antarctic as ranges over 40' at Kew. 

 A single year's records in such latitudes at the ' Discovery's ' winter 

 quarters is likely to supply as many large disturbances as the records 

 of a generation in the south of England. This is one reason why so 

 much importance attaches to trustworthy observations with self- 

 recording magnetographs during scientific expeditions to high lati- 

 tudes. 



§ 6. The daily amplitude of irregular magnetic changes, like that 

 of the regular diurnal inequality, is variable throughout the year, 

 but the seasonal variation is usually different in the two cases. This 

 is shown by Table III. 



Table III. — Annual Variation in Inequality and Absolute Declination 

 Ranges at Kew, omitting Highly Disturbed Days (1890-1900). 



Inequality range .... 

 Absolute range .... 

 (Absolute range -r- Inequality range) 



Winter. 



Equinox. 



Summer. 



Each of the three seasons contains 4 months, March, April, 

 September and October being included under " Equinox." 



The diurnal inequality range, which practically depends only on 

 the regular changes, is distinctly largest in summer. But the absolute 

 range, which depends greatly on the irregular changes, is largest in the 

 equinox, and its winter value is both relatively and absolutely very 



