Section III. 1918 [99] Trans. R.S.C. 



A Comparative Study of Magnetic Declination at Agincourt and 

 Meanook, During the Year 1917. 



By W. E. W. Jackson, M.A. 



Presented by Sir Frederick Stupart, Kt., F. R.S.C. 



(Read May Meeting, 1918). 



In July of 1916 there was established at Meanook, Alberta, a 

 Magnetic Observatory for the purpose of securing a continuous photo- 

 graphic record of the Magnetic Declination. The first calendar year's 

 record was completed on December 31st, 1917, and a preliminary 

 analysis of the results obtained are here presented, together with a 

 comparative analysis of the results obtained at Agincourt The 

 Meanook station is located in Longitude 113° 21' W and Latitude 

 54°37'N, and the Agincourt station in Longitude 79° 16' W and 

 Latitude 43° 47' N. 



At Meanook 105th Mean Time is used, at Agincourt 75th Mean 

 Time, and the clocks are compared daily with chronometers whose 

 errors are allowed to accumulate and Avhose rates are determined 

 weekly by telegraph. By the addition or subtraction of small weights 

 to the pendulum of the time clocks they are kept within a few seconds 

 of the true standard time, and are provided with electrical contrivances 

 to mark the hours on the photographic records. 



The ordinates are measured for each hour of the day, and the mean 

 of the 24 hourly values is taken as the mean for the day, and the mean 

 of these means for each day of the month is the mean for the month. 

 The base line values are determined from absolute Declination observ- 

 ations made weekly. The resultant mean Declination for each month 

 of the year at each place is given in table I, Easterly Declination is 

 called positive ancJ Westerly Declination negative. Assuming that 

 the non-cyclical variation progresses through the year uniformly, then 

 by taking the difference between the values for December 1916 and 

 December 1917 and distributing it uniformly we obtain the annual 

 variation, which is also given in table I. 



At Agincourt the annual Variation shows maximum Easterly 

 movement in the summer and maximum Westerly movement in the 

 winter, whilst at Meanook, the very opposite obtains, that is, there is 

 a diverging of the lines of Force between the two places in the summer 

 which could be produced by an annual pulsation in the earth magnet 

 which carries the North Magnetic Pole nearer the surface along the 



