A SIMPLE DESCEIPTION OF THEiMICROSCOPE 13 



the formation of the images. An enlarged picture of an object 

 placed upon the stage (D) is formed in the neighborhood of 

 the eyepiece at U, and the eyepiece again magnifies this image, 

 projecting the light into the eye as if it came from an object 

 situated at V. 



The eye, when placed in a small area (T) through which all syepieoe. 

 light passes, and which is known as the eyepoint, sees the final 

 picture of the object as if it were a real object placed at V, 

 10 inches from the eye. 



It is assumed for convenience of measurement that this picture virtual 

 is actually 10 inches away, though it may be formed at a some- "°'^*" 

 what different position according to the adjustment or condition 

 of the observer's eye. Whether the virtual image is actually 

 at 6, 10, or 20 inches is of no importance. It makes no 

 difEerence to the size of the picture, because when the virtual 

 image is formed farther away it becomes proportionally larger. 

 In Fig. 4, if E is the eye and 0' 0" are objects of different 

 sizes, they produce the same size pictures in the eye if placed 

 at such distances that they 

 subtend the same angle. 



The magnifying power of 

 the microscope will depend 

 upon the size of this final 

 image formed at V (Fig. 1) 

 compared with the size of the 

 object being examined. In this 

 connection it should be under- _ 



stood that if a microscope is said to magnify' 100 diameters, 

 it means that the picture that is seen is 100 times as long and 

 100 times as wide as the object would appear if it were 

 taken from the stage (D, Fig. 1) and placed in the position V, 

 10 inches from the eye. 



In order to express how much larger an object appears 

 when seen through the microscope than when seen by the naked 

 eye, a standard distance must be taken, because an object appears 

 to the naked eye to be of different sizes at difierent distances. 

 A sixpence is almost invisible at a distance of 100 yards, but it 

 is a large object at 8 inches. Therefore, some standard 

 must be taken for comparison purposes, and 10 inches has 

 been universally adopted. The magnifying power of a micro- 

 scope always denotes the relative size of the picture com- 

 pared with that of the original object when placed 10 inches 

 from the eye. 



If a microscope has a magnifying power of 100, such magnifi- d^«™*„, 

 cation may be produced by different methods. The object obtaining 

 glass may magnify the object twenty times in the primary image, ^^^^ 

 and the eyepiece increasing the primary image five times will 

 give a total of a hundred. This magnification may also be pro- 



