CHAP, ii.] ELECTRICITY AND MAGNETISM. 



Inclination, and total magnetic force at a number of 

 important places, the values being approximately true 

 for the year 1880. 



TABLE OF MAGNETIC DECLINATION AND INCLINATION 

 (for Year 1880.) 



138. Intensity. Three things must be known in 

 order to specify exactly the magnetism at any place ; 

 these three elements are : 



The Declination ; 



The Inclination, and 



The Intensity of the Magnetic Force. 



The magnetic force is measured by one of the 

 methods mentioned in the preceding Lesson. Its 

 direction is in the line of the dipping-needle, which, like 

 every magnet, tends to set itself along the lines-of-force. 

 It is, however, more convenient to measure the force 

 not in its total intensity in the line of the dip, but to 

 measure the horizontal component of the force, that 

 is to say, the force in the direction of the horizontal 

 compass -needle, from which the total force can be 



