Mirrors of Magnetism. 217 



hinged strip upon which the other solenoid was placed, the 

 angle of inclination being the same for both solenoids (fig. 5). 



Fig. 5. 



The angle was altered step by step from to 90 degrees, and 

 in all cases the iron plate produced the same effect as its 

 image within limits not greater than those shown in the 

 previous table. It was, however, only when the solenoid 

 was placed at the end of the hinged strip nearest the iron 

 plate that readings of any value could be obtained, as small 

 dislocations in the position of the coil laterally were apt to 

 produce changes of reading comparable with those due to 

 considerable changes in angle. At distances greater than 

 5 centim. the iron had very little effect. The search-coil 

 during these experiments was moved about to different 

 positions both inside and outside the solenoid, preference 

 being given to the most sensitive positions. 



Then the effect of differently-shaped solenoids was tried. 

 A long narrow one and a wide flat one were used with similar 

 effects, so far as they could be measured. 



There is a difference between the magnetic reflexion of an 

 iron plate and the optical reflexion of a mirror in the following 

 respect : an optical image has those of its lines which are at 

 right angles to the mirror reversed while those parallel to the 

 mirror are not reversed. For instance, if we hold a magnet 

 with its north end pointing from us and towards a mirror, 

 the optical image of it will have its North end pointing 

 towards us (fig. 6). But in the case of a magnetic image 

 this is inversed: the magnetic image has its South end point- 

 ing towards us. In fact the reflexion of a North end is a 

 South end. If, however, we look at the reflexion of the cur- 

 rents flowing in the solenoid instead of at the sign of the pole 

 qf the solenoid, we see that laws of the optical case hold good, 



