CHAPTER IV 



MAGNIFICATION AND MICROMETRY 



APPARATUS AND MATERIAL FOR THIS CHAPTER 



Simple and compound microscope (I 156, 158); Steel scale or rule divided to 

 millimeters and Aths ; Block for magnifier and compound microscope ($ 156, 160); 

 Dividers (§ 156, 160); Stage micrometer ($ 159); Wollaston camera lucida ( \ 160); 

 Ocular screw-micrometers (Figs. 106-107); Micrometer ocular (Figs. 104-105). 

 Abbe camera lucida (Fig. 101). Necturus red blood corpuscles (I 168). 



§ 154. 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 apparent size is ob- 

 tained by measuring the virtual image (Figs. 21, 38). The object for 

 determining magnification must be of known length and is designated 

 a micrometer (§ 159). In practice a virtual image is measured by the 

 aid of some form of camera lucida (Figs. 97, 101), or by double vision 

 (§ 156). 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 magnified, 2 mm., the amplification must be 

 40 -4- 2 = 20, that is, the apparent 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 the scale at which a micro- 

 scopical or histological drawing is made, the word magnification is fre- 

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

 drawing would mean that the figure or drawing is 450 times as large 

 as the object. 



§ 155. Magnification of Real Images. — In this case the mag- 

 nification 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 (§ 53), it will be 

 remembered that it forms a real image on the ground glass placed on 

 the top of the tube, and that this real image could be looked at with the 



