THE MAGNETISM OF IRON. 



69 



in Fig. 330. These two agents acting together produce a mag- 

 netic field at / which is represented by the line 3 which is the 

 resultant of I and 2. 



Resolution of a magnetic field into components. Consider a 

 magnetic field whose direction and intensity at a point p, Fig. 



Fig. 33a- 



Fig. 33b. 



, is represented by the line R. It is often convenient to con- 

 sider that part of the field which acts in a given direction ; thus, 

 J-f, Fig. 33^, is called the horizontal component of R, and V 

 is called the vertical component of R. 



38. Magnetic flux. Let a (expressed in square centimeters) 

 be an area at right angles to the velocity of a moving liquid and 

 let v (expressed in centimeters per second) be the velocity of 

 the liquid. Then av is the flux of the liquid across the area in 

 cubic centimeters per second. Thus, if v is the velocity of 

 liquid in a pipe and a is the sectional area of the pipe, then av 

 is the number of cubic centimeters of liquid discharged per 

 second by the pipe. 



Similarly, the product of the intensity H of a magnetic field 

 and an area a at right angles to H is called the magnetic flux 

 across the area ; that is, 



(18) 



in which <I> is the magnetic flux across an area of a square centi- 

 meters which is at right angles to a magnetic field of which the 

 intensity is H gausses. 



Representation of the magnetic flux across an area by the number 

 of lines of force which pass through the area. Imagine a surface 



