28(J orncs. 



again magnified six times; that is, six times by the 

 object-glass, and six times by the eye-glass; which, 

 multiplied into one another, makes thirty-six times; 

 and so much is the object magnified in diameter 

 more than what it appears to the bare eye, and 

 consequently thirty-six times thirty-six, or 1296 

 times in surface. 



But because the extent or field of view is very 

 small in this microscope, there are generally two 

 eye-glasses placed sometimes close together, and 

 sometimes an inch asunder; by which means, 

 although the object appear less magnified, yet the 

 visible area is much enlarged by the interposition 

 of a second eye-glass, and consequently a much 

 pleasanter view is obtained. 



A Q is the body or internal part, which is move- 

 able up and down in C D (Fig. 2.) an external 

 case of wood, brass, or silver. E, one of the three 

 pillars which support the instrument. F, a plate 

 fixed (horizontally) to the legs, usually called the 

 stage: there is a hole in the central part, in which 

 glass, and other parts of the apparatus, are placed, 

 with objects to be viewed. H, an illuminating or 

 reflecting speculum. I, the foot of the instrument. 

 Q, a brass button, or case, to hold the magnifier. 



In this compound microscope, there are generally 

 three (sometimes four) glasses employed to pro- 

 duce the effect, viz. 1. The magnifying lens at Q, 

 which makes a large image in the upper part of the 

 small object below. 2. A large lens at B, called 

 the body-glass, which is the cause of a larger field 

 of view. 3. An eye-glass at A, by which we view 

 the enlarged image of the object in its focus. 



The magnifying power in all optical instruments 

 depends upon this one principle, that every object 

 is apparently greater or less, in proportion as it is 



