Ch. V] 



MEASURING WITH THE MICROSCOPE 



149 



Micrometry 



§ 244. Micrometry is the determination of the size of objects by 

 the aid of a microscope. 



Micrometry with the Simple Microscope 



§ 245. With a simple microscope (1), the easiest and best way 

 is to use dividers and then with the simple microscope determine 

 when the points of the dividers 

 exactly include the object. The 

 spread of the dividers is then 

 obtained as above (§ 230-231). 

 This amount will be the actual 

 size of the object, as the mi- 

 croscope was only used in help- 

 ing to see when the divider 

 points exactly enclosed the 

 object. 



(2) One may put the object 

 under the simple microscope and 

 then, as in determining the 

 power (§ 230), measure the im- 

 age at the standard distance. 

 If the size of the image so meas- 

 ured is divided by the magnifi- 

 cation of the simple microscope, 

 the quotient gives the actual 

 size of the object. One might 

 use the eikonometer also 



(§ 254)- 



Use a fly's wing or some other 

 object of about that size and try 

 to determine the width in the 

 two ways described above. If 

 all the work is accurately done 

 the results will agree. 



Fig. 94. Field of the Microscope 

 Showing the Lines and the Record- 

 ing Comb of the Filar Microm- 

 eter (Fig. 93). 



C The recording comb. Each tooth 

 represents a complete revolution of the 

 drum (fig. 93). 



//,// The fixed cross lines. 



tnl, ml The movable line. 



The arrow shows that the movable 

 line can be moved in both directions. 



Object, the full movable line (ml) 

 shows it at one edge of the object and 

 the broken line shows it at the other 

 edge of the object. The intervening 

 teeth of the comb show that the screw 

 was turned two whole revolutions and 

 the recording drum showed 90 divisions, 

 making two and nine tenths revolutions 

 of the drum to carry the movable line 

 from one edge of the object to the other. 



