MAGNETISM AT HALIFAX, AUGUST, 1904. — DIXON. 251 



by order of the Surve3^or General of New Brunswick in October, 

 1874. In the year 1898, a magnetic survey of North Carolina 

 was made by the U. S. Coast and Geodetic Survey and the 

 North Carolina Geological Surve3^ During the survey meridian 

 lines were established in the county towns, and the county 

 commissioners were so impressed with the value of the work 

 that in many cases they paid the field expenses of the survey. 



Daily Variations in Declination. 

 Besides the great secular changes in declination Ave find 

 several small changes — periodic or irregular. The first of these 

 — the Daily Variation — was discovered in 1722 by Graham 

 who, from a series of several hundred observations made at 

 Loudon, found that the declination varied during the day. The 

 average value of the arc through which the needle swings is 

 about eight minutes, the true declination occurring about 10.30 

 a. m. and 8 p. m. At Fort Conger in Grinnell Land an extra- 

 ordinary value of 1° 40' has been found for the daily variation. 



Annual Variation. 



The second of the small periodic changes to which the 

 declination is subject, is that known as the Annual Variation, 

 and is found by tabulating the monthly values corrected for the 

 secular changes. The average value f^r Toronto is about 

 half a minute. There is also a Lunar Variation, but this is even 

 smaller than the annual, being only about 15 seconds from the 

 mean. 



Irregular Changes in Declination. 



Besides these periodic changes in declination, it has been 

 found that owing to so called magnetic storms, the magnetic 

 needle is often violently aflfected. In these disturbances the 

 maximum deflections of the needle from the mean position range 

 from about 20' and a variation of 2° observed at Mantilik in 

 1896*^' and an extraordinary deflection of 20° 1' recorded by 



(1) Lat. 64° 53' .5 N., long. 66* 19' .5 W. 



