ELEMENTARY EXPERIMENTAL PHYSIOLOGY 15 



shine on the front of the model. Using the mirror with a hole in 

 the centre, reflect light into the model eye, and look into it through 

 the hole. Begin at a distance of 2 feet from the eye, and approach 

 it keeping the light reflected into it. Gradually the mark on the 

 paper becomes distinctly visible. Is it erect or inverted ? (The 

 observer's eye must be kept accommodated for distant vision.} 



E 1 ^ E 



M 



FIG. 3. Ophthalmoscope to show the formation of the image in the direct 



method. 



(b) Indirect Method. With the mirror about 3 feet from the 

 model eye reflect the light into it. Now insert a biconvex lens at 



M 



FIG. 4. Ophthalmoscope to show the formation of the image in the indirect 



method. 



about 4 or 5 inches in front of the model, and try to see the image 

 of the mark on the paper. Is it erect or inverted ? 

 The human eye may be examined in the same way. 



B. VISION WITH ONE EYE 

 I. The Focussing Mechanism 



1. The Formation of Images by a Lens. 



METHODS. A. In a dark room, using a candle, study the 

 formation of images on an obscure glass screen behind a lens. 



1. Where is an object held above focussed on the screen and 



