Highly Magnified Images. By J. W. Gordon. 



23 



of the antipoint on each side of the true boundary, and that whereas 

 the light intensity curve shows an uninterrupted progression from 

 edge to edge of the fringe, it is not so with the phase change. On 



-e- 



§ dp § § <b 



,. 1 I I 



Fig. 19. 



the contrary the phase, proceeding by an uninterrupted change, 

 leaches at the point A, which stands vertically over the boundary, 

 its permanent value ; then, continuing the change as far as the 

 point B, the phase there attains its highest value, and from that 

 point by a retrogressive change it falls back until at the brighter 

 edge of the fringe it reaches once more the permanent value, 

 which it retains over the rest of the illuminated area. The result 

 is, as shown at wf in the figure, a wave-front having a recurved 

 or corrugated form. Thus the two parts wf x and wf 2 will be propa- 

 gated in different directions, one towards the left the other towards 

 the right of the diagram, and we shall have two conical wave-fronts, 

 the one expanding while the other contracts, each in its turn form- 

 ing a ring about the other — the one giving rise to a broad ring and 

 large bright dot focus, the other to a narrow ring and exquisitely 



Fig. 20. 



small focal bright dot. Fig. 20 is a drawing depicting these pheno- 

 mena, and they are this evening demonstrated by means of a 

 suitable telescope and artificial star. 



