INTRODUCTION TO PHYSIOLOGICAL OPTICS 423 



The image of the circular aperture in the dia- 

 phragm will be a vertical line with blurred con- 

 vex ends. 



Turn the cylinder so that the curvature shall 

 be in the vertical meridian. 



The image will be a horizontal line with 

 blurred convex ends. 



2. Place the diaphragm with horizontal slit in 

 the lantern. Throw parallel rays into the box. 

 Place the cylinder in the axis of the pencil with 

 its curvature vertical. 



The horizontal line is a fusion of illuminated 

 points. From each point rays diverge in all 

 directions. Those passing from any point in 

 vertical planes through the cylinder convex in 

 its vertical meridians will be -focussed by the 

 convex surface in a corresponding point in the 

 image. The overlapping of such points will form 

 a horizontal line with clear upper and lower 

 edge. The rays passing from any point in the 

 illuminated line in horizontal planes through 

 the cylinder with vertical curvature will be 

 refracted by plane glass surfaces and will not 

 come to a point but will form a faint horizontal 

 line. The overlapping in the image of the 

 bright points in which unite the rays passing 

 in vertical planes and the faint horizontal lines 

 formed by rays passing in horizontal planes will 



