CHAPTER IV 



MAGNIFICATION AND MICROMETRY 



APPARATUS AND MATERIAL FOR THIS CHAPTER 



Simple and compound microscope (fj 172, 174); Steel scale or rule divided 

 to millimeters and \\ Block for magnifier and compound microscope (§ 172, 

 176); Dividers (§ 172, 176); Stage micrometer (§ 175); Wollaston camera lucida 

 (jS 176); Ocular screw-micrometers (Figs. 118-120); Abbe camera lucida (Fig. 

 114). Necturus red blood corpuscles (g 184). Eikonometer (J 195). 



§ 170. The Magnification, Amplification or Magnifying 

 Power of a simple or compound microscope is the ratio between 

 the real and the apparent size of the object examined. The appar- 

 ent size is obtained by measuring the virtual image (Figs. 26, 43). 

 For determining magnification the object must be of known length 

 and is designated a micrometer (§ 175). In practice a virtual image 

 is measured by the aid of some form of camera lucida (Figs. 108, 

 114), or by double vision (§ 172). As the length of the object is 

 known, the magnification is easily determined by dividing the 

 apparent size of the image by the actual size of the object. For 

 example, if the virtual image measures 40 mm. and the object mag- 

 nified, 2 mm., the amplification is 40-^2=20, that is, the appar- 

 ent size is 20 fold greater than the real size. 



Magnification is expressed in diameters or times linear, that is 

 but one dimension is considered. In giving a scale at which a micro- 

 scopical or histological drawing is made, the word magnification is 

 frequently indicated by the sign of multiplication thus : X 450, upon 

 a drawing means that the figure or drawing is 450 times as large as 

 the object. 



§ 171. Magnification of Real Images.— In this case the 

 magnification is the ratio between the size of the real image and the 

 size of the object, and the size of the real image can be measured 

 directly. By recalling the work on the function of an objective 



