400 



ON MAGNETS. 



427. To get the direction of the molecule let us draw a sphere 

 whose radius is equal to the reaction of the medium, and take a 

 length OS from the centre, equal and opposite to the strength of the 

 field (Fig. 88). 



- 



HOO "I '0 



Fig. 88. 



A molecule, the axis of which was originally directed along the 

 line OP, is subject to two forces SO and OP, the resultant of which 

 is SP. If- the resultant S is in the interior of the sphere that is, if 

 the reaction of the medium is greater than the strength of the field 

 the axes of the deviated molecules will be still in any direction 

 whatever, but no longer uniformly. 



If the force of the field is greater than the reaction of the 

 medium, the point S is beyond the sphere (Fig. 89), and the axes of 

 the deviated molecules are all comprised within the cone TST 

 tangential to the sphere. 



Fig. 89. 



Let a be the original inclination of the axis of a molecule to 

 the axis x, 



9 the final inclination, 



/3 the deflection a - 6, 



R the resultant of the magnetising force X, and of the reaction 

 D of the field. 



