METHODS AND RESULTS OF TORONTO OBSERVATIONS. 73 



METHODS AND RESULTS OF TORONTO OBSERVATIONS. 



BY LIEUT. ANDREW GORDON, R.N., DEPUTY SUPERINTENDENT 

 METEOROLOGICAL SERVICE OF CANADA. 



The Toronto Observatory was one of the five which were estab- 

 lished by the Imperial Government with a view to extending the 

 knowledge of magnetic phenomena. 



The elements on which the determination of the earth's mag- 

 netic force is based are the declination, inclination, and intensity. 

 The declination determines the direction of the force referred to the 

 plane of the meridian (astronomical.) The inclination determines 

 its direction in reference to the horizontal plane. If in addition to 

 these quantities we know the measure of the intensity expressed in 

 some absolute unit, the force will be completely determined. The 

 absolute unit which has been adopted by English observers is for 

 mass, the grain ; for space the foot ; and for time the second. The 

 idea may be readily grasped from the following. When two south 

 poles, distant one foot from each other, are charged to equal strength, 

 and repel one another with a force which, if continued uniform, 

 would produce in one second a velocity of one foot per second in a 

 mass of one grain, each pole is said to be charged with unit magnetic 

 force. 



For the purpose of detecting and examining the more minute 

 changes in the magnetic force a different system of elements is em- 

 ployed, the intensity being resolved into two portions in the plane of 

 the magnetic meridian, one portion horizontal and the other vertical. 

 It is readily seen that these two components may be substituted for 

 the total intensity and the inclination, being connected with them 

 by the relations 



X=RcosI; Y=RsinI 



where X and Y are the horizontal and vertical components of the 

 force, and R and / the intensity and inclination respectively. Varia- 

 tions in R and I are then expressed in terms of the variations in 

 X and Y. 



Of these elements the declination was the first to be examined, 

 and I shall now treat briefly of it. The declination called by sailors 

 the variation has been the subject of investigation for hundreds of 



