220 Dr. S. P. Thompson and Mr. Miles Walker on 



material are inclined to each other at 

 an angle of 60 degrees, and the North Fig. 11. 



pole of a magnet placed evenly between 

 them, one would expect to get between 

 the plates exactly the same distribution 

 of field as if there were six poles, three 

 norths and three souths, spaced alter- 

 nately and evenly round the line of 

 intersection of the plates. It may, 

 however, be said to those who would 

 care to try this experiment, that they 



must use a point pole of much greater N 



strength than 40 units, or plates much m 



more susceptible than iron if they hope S 



to be at all successful. 



The close connexion between the effect of an iron plate 

 magnetically and that of a mirror optically naturally makes 

 us ask what would be the effect of a curved plate ? Would it 

 give magnified or diminished images like a concave or convex 

 mirror, and what would be the position of these imnges with 

 regard to the object ? 



If we take the case of spherical curvature, and consider the 

 iron as being infinitely susceptible, the answer to these 

 questions can be determined theoretically from the laws of 

 magnetic potential. All the formulas relating to electric 

 images already known are applicable to magnetic images. 



If we consider two points A and B at which are placed 

 two poles respectively, of the strengths +m 1 and — m 2 , the 



Fiff. 12. 



magnetic potential at a point C due to m 1 is — where 7^= AC, 



rwy\ 



and that due to — m 2 is where ^ = BC. 



