CH. /] 



MICROSCOPE AND ACCESSORIES 



Hold the simple microscope directly toward the sun and move it 

 away from and toward a piece of printed paper until the smallest 

 bright point is obtained. This is the burning point or focus and as 

 the rays of the sun are nearly parallel, the burning point represents 

 approximately the principal focus (Fig. n). The above and follow- 

 ing operations are more easily accomplished if the lens is supported as 

 in Fig. 20. 



Without changing the position of the magnifier or paper look into 

 the magnifier, holding the eye close to the upper surface and the 

 letters on the paper may be seen, but they will appear much sharper 

 to the eyes of most people if the magnifier is brought nearer to the 

 paper, that is so that the printed paper is within the principal focal 

 distance (Fig. 15 and 16). 



Fig. 1 6 A. Figures of a normal (emme- 

 tropic], a far sighted (hyperopic) and a short 

 sighted (myopic] eye to show that when the eye 

 is at rest the normal eye (E) focuses parallel 

 rays on the retina while the far-sighted eye (//) 

 focuses parallel rays beyond the retina. The 

 short sighted eye (M) focuses parallel rays in 

 front of the retina. The dotted lines show that 

 in the hyperopic eye the rays must be converging 

 to come to a focus on the retina while with the 

 myopic eye they must be diverging. 



After getting as clear an image as possible by focusing the simple 

 microscope, raise the magnifier until the letters are at a distance a 

 little greater than the principal focal distance. Look into the magni- 

 fier and note the clearness of the virtual image, then slowly elevate 

 the head above the magnifier and when the eye is about 60 to 100 

 centimeters above the lens a real image can be seen. That is an 

 image in which the letters are inverted as with the objective of the 

 compound microscope (see 53). If the magnifier is raised somewhat 

 so that the printed letters are markedly without the principal focus the 

 real image will be seen more clearly especially if the eye is brought 

 somewhat near the magnifier. The above experiments show two 

 things. 



