414 



Special Reports 



NO. 4. DOMINION OBSERVATORY, OTTAWA, CANADA. 



Comparisons of the instruments of the Dominion Observatory were secured at the 

 Standardizing Magnetic Observatory of the Department of Terrestrial Magnetism at 

 Washington, D. C, in November and December 1915, by Observers C. A. French, of 

 the Dominion Observatory, and H. W. Fisk and W. F. Wallis of the Department. The 

 instruments used were D. O. magnetometers Tesdorpf No. 1977 and Cooke No. 15, 

 D. 0. earth-inductor Toepfer No. 1911, D. O. dip circle Dover No. 145, C.I.W. 

 standard magnetometer No. 3, and C. I. W. standard earth-inductor Schulze No. 48. 

 The observations were made at the 2 tripod stations N m and S m , and at the 3 piers N e , 

 S e , and E m , of the Standardizing Magnetic Observatory; a full description of this Observ- 

 atory and a plan showing the locations of the stations used is given in Volume II, 

 Researches, Department of Terrestrial Magnetism, pages 199 to 200 and Fig. 9. The 

 galvanometers used for the observations with the earth inductors were mounted on 

 piers N , S g , and E. 



Declination observations with magnetometer Tesdorpf No. 1977 were made both 

 with magnet 10 and with magnet 14; magnet 10 has been used at all field stations 

 occupied with this instrument by the observers of the Dominion Observatory. Because 

 of the range in the results of the declination-comparisons at Washington, Ottawa, and 

 Agincourt, 1908-1915, special tests and observations (Tables 4D and 4E) were made 

 at Washington in November 1915 to determine whether there was any magnetic impurity 

 in the copper dampers, or in the brass of the magnet house, of this instrument. These 

 tests showed that, for normal positions of dampers, there is no effect on account of 

 possible magnetic impurity of the metal, even when the suspended magnet is used at 

 highest-possible or lowest-possible positions in its housing. The variation of the declin- 

 ation-correction for magnetometer No. 1977 may have to be ascribed to slight displace- 

 ments of the reflecting mirror mounted in the hollow magnet, or to the fact that the 

 short suspension bars of the magnet may not invariably take the same positions in the 

 suspension hook. 



Table 4A. 



-Results of Declination Comparisons at the Standardizing Magnetic Observatory of the Department of 

 Terrestrial Magnetism at Washington, 1915. 



1 All values are referred to station N m ; N m = Sm+0'.5, as derived from this series. Observers: D. O. No. 1977, C. A. 

 French of the Dominion Observatory; C. I. W. No. 3, H. W. Fisk of the Department of Terrestrial Magnetism. 

 > These are values obtained with C. I, W. No. 3 referred to I. M. S.; I, M. S. C. I. W. No. 3= -O'.l. 



