Comparisons of Magnetic Standards, 1915-21 419 



{Ad) I. M.S. -Dominion Observatory (Cooke magnetometer No. 15)= +0.00106// (1915). 

 (4c) I. M. S. Dominion Observatory (Earth inductor No. 1911, by Toepfer)= 0'.25 



(1915). 

 (4/) I. M. S. Dominion Observatory (Dover dip circle No. 145, needles 1 and 2)= +0'.6 



(1915). 

 (4g) I. M. S. Dominion Observatory (C.I. W. universal magnetometer No. 20)"= 0'. 7 



(1915-1921). 

 {Ah) I. M. S. Dominion Observatory (C.I.W. universal magnetometer No. 20)"= 



0.00023//- 0- 1915.19) 0.00010// (Mar. 1915-June 1921, constants of March 25, 



1916). 

 (4i) I. M. S. Dominion Observatory (C.I.W. universal magnetometer No. 20)" = 



0.00010// (July 1921, constants of July 31, 1921). 

 (4/) I. M. S. Dominion Observatory (C.I.W. universal magnetometer No. 20)"= 0'. I 



(1915-1921). 



Previous Comparisons of the Dominion-Observatory Instruments. 



Simultaneous comparisons in declination and in horizontal intensity were made on 

 April 7 and 9, 1908, between magnetometers D.O. No. 1977 and C.I.W. No. 3, at 

 stations A m and C m) Washington, D. C. (see page 172 of Volume I, Researches, Depart- 

 ment of Terrestrial Magnetism, for descriptions of stations); the station-differences 

 having been determined from other observations at the time, the stations were not 

 exchanged. From 11 sets of declination comparisons, the mean value of [I. M.S. 1977 

 (magnet 10)] was found equal to +5'. 2. From 5 sets of horizontal-intensity comparisons, 

 it was found that the mean value of [I. M.S. 1977 (magnets 46 and 10)] = -0.00258//. 

 This value agrees well with that determined at Washington in 1915; too great weight, 

 however, can not be given the 1908 result, since the reductions for magnetometer No. 

 1977 had to be based on the mean value of distribution coefficient derived from only 

 the 5 sets of comparison-observations. 



Dr. O. Klotz, director of the Dominion Observatory, courteously supplied the 

 results of declination-comparisons at Ottawa, 1912-1915, between D.O. magnetometers 

 Tesdorpf No. 1977 and Cooke No. 15, as also the results of inclination-comparisons at 

 Ottawa, 1912-1915, between D.O. earth inductor Toepfer No. 1911 and D.O. dip circle 

 Dover No. 145 (needles 1 and 2). The observations for these comparisons were made 

 alternately on the north and south piers in the absolute magnetic observatory, without 

 exchange of stations, except in 1914, when an exchange was made for the declination- 

 comparisons, and the station-difference was found to be O'.O. Table 4J summarizes 

 the results of these comparisons. 



Dr. Klotz likewise supplied the results of comparison-observations, made in the 

 Absolute Observatory at Agincourt from 1908-1915, between the instruments of the 

 Dominion Observatory and those of the Agincourt Observatory. All observations 

 with D.O. magnetometer, Tesdorpf No. 1977 (magnet 10 for declination, except as noted, 

 and magnets 46 and 10 for horizontal intensity), were made on pier B, and the Agincourt- 

 values were derived from eye-readings of the variometers. All observations with D.O. 

 dip circle, Dover No. 145 (needles 1 and 2), were made on pier E, and all observations 

 with the Agincourt dip circle, Dover No. 200 (needles 1 and 2), were made on pier D. 

 As stations were not exchanged, it was necessary to assume, in deriving the results of 

 Tables 4K, 4L, and 4M, that the station-differences were negligible. The constants of 

 magnetometer No. 1977 were those adopted for each year by the Dominion Observatory 

 using the mean value of P' (Q assumed zero) for the year, except that for 1908 the value 

 of P' derived from a set of observations was used to reduce that set; for 1915 the adopted 

 constants for 1914 were used. 



See pp. 401-402. 



