142 



EXPERIMENTAL PHYSIOLOGY. 



surface, lies along such a line. It is reflected back along the path 

 on which it came (since i = o in this case, r must also =o). PA, 

 another incident ray from P, is so reflected (ray AB) that the angle 

 of incidence (i) equals the angle of reflection (r). The place (P') 

 where this crosses the reflected ray PC is the image of the point P, 

 from which these and all other reflected rays from P appear to 



M 



FIG. 39. To show refraction of rays passing from air into water. 



come. The construction of the image, Q', of the other limiting 

 point, Q, is similar. The rays in this case actually pass through 

 the image from which they seem to come, and the image is there- 

 fore called a REAL one. Real images are always inverted. 



Refraction. 



Refraction at a Plane Surface. When a ray of light passes 

 from air into a denser medium such as glass or water, the direction 



