MICROSCOPE AND ACCESSORIES. 



[CH. I. 



If now it is prolonged it will cross the secondary axis above the lens for a real 

 image and below for a virtual image. The crossing point of these lines determines 

 the position of the corresponding part of the image. Commencing with any point 

 of the object the corresponding point of the image may be determined as just 

 described, and converse^ commencing with the image corresponding points of 

 the object may be determined. 



SIMPLE MICROSCOPE : EXPERIMENTS. 



§ 9. Employ a tripod or other simple microscope, and for object a 

 printed page. Hold the eye about two centimeters from the upper sur- 

 face of the magnifier, then alternately raise and lower the magnifier 

 until a clear image may be seen. (This mutual arrangement of micro- 

 scope and object so that a clear image may be seen, is called focusing). 

 When a clear image is seen, note that the letters appear as with the 

 unaided eye except that they are larger, and the letters appear erect 

 or right side up, instead of being inverted, as with the compound mi- 

 croscope (§ 10, 49). 



i** 



Fig. 16. Diagram of the simple microscope show- 

 ing the course of the rays and all the images, and 

 that the eye forms an integral part of it. 



A 1 B\ The object within the principal focus. A* 

 B 3 . The virtual image on the same side of the lens 

 as the object. It is indicated with dotted lines, as it 

 has no actual existence. 



B 1 A' 1 . Retinal image of the object (A 1 B<). The 

 vii tual image is simply a projection of the retinal 

 image in the field of vision. 



Axis. The principal optic axis of the microscope 

 and of the eye. Cr. Cortieaofthe eye. L. Crystal- 

 line lens of the eye. R. Ideal refracting surface at 

 which all the refractions of the eye may be assumed 

 to take place. 



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 on the paper is obtained. This is the burning point 

 or fonts, and as the rays of the sun are nearly parallel, the burning 



