Comparisons of Magnetic Standards, 1915-21 



Table IE. Results of Horizontal- Intensity Comparisons at the Agincourt Observatory, 1916. 



401 



1 All values are referred to pier E, which is used by the Observatory for the horizontal-intensity observations; = 

 F 12.47 as derived from this series. Observers were: magnetometer No. 98, W. Menzies; magnetometer No. 15, W. E. W. 

 Jackson. 



2 These values were obtained using constants for magnetometer No. 98 as determined in February 1911 at Agincourt. 



3 These values were obtained using constants for magnetometer No. 15 as determined during February and March 

 1910 at Washington. 



From Tables ID and 1A we have, since E = A + 0'.38: 



(</) Agincourt (Toronto declinometer) M. S. magnetometer No. l5 = +0'.4. 

 (e) I.M.S.-M.S. magnetometer No. 15= 0'.9. 



Hence we get: 



(/) I. M. S. Agincourt (Toronto declinometer) = I '.3. 



From Tables IE and IB we have: 



(g) Agincourt (Elliott magnetometer No. 98) -M.S. magnetometer No. 1 5 =- 0.00029//. 



(/i) I.M.S.-M.S. magnetometer No. 1 5 = +0.00007//. 

 Hence we get: 



(i) I. M.S. -Agincourt (Elliott magnetometer No. 98) = +0.00042// (weight 1). 



Indirect Comparisons, 1915-1921. 



In May and June 1921, at the request of Dr. Otto Klotz, director of the Dominion 

 Observatory, C. I.W. universal-magnetometer No. 20, belonging to the Dominion 

 Observatory, was compared at the Standardizing Magnetic Observatory of the Depart- 

 ment at Washington. It was found that, by reason of change in the moment of inertia 

 of the long magnet and its stirrup in the course of field work since the previous deter- 

 mination at Washington in March 1916, the correction on I. M.S. in intensity had 

 changed 0.00055//, i.e., from -0.00023// to -0.00078//. The actual difference in 

 observed moments of inertia determined at the same time as the two comparisons was 

 equivalent to 0.00076//, in good agreement with the observed change of differences on 

 I. M.S. The correction on I. M.S. in declination, 0'.7, observed in 1921, was identical 

 with the earlier one. 



This magnetometer was also compared before and after each summer's field cam- 

 paign with I. M.S. as defined at Agincourt by the relations above given (see p. 400). 

 Dr. Klotz has communicated the results of these comparisons, made by Observer C. A. 

 French of the Observatory staff; they are summarized in Table IF. The individual 

 results, except for the October 1918 comparisons, and the mean results show excellent 

 agreement and, accordingly, constancy of adopted I. M.S. in declination and horizontal 

 intensity, well within the errors of observation, both at Agincourt and at Washington. 



Dominion Observatory universal-magnetometer C. I. W. No. 20 being of the dip- 

 circle type can not be considered of precision equal to the standard earth-inductors 



See foot-note 3 on p. 400. 



