282 



Methods in Plant Histology 



Measuring with the Ocular Micrometer. A stage micrometer 

 and an ocular micrometer are necessary. A stage micrometer should 

 be ruled in tenths and one-hundredths of a millimeter. It does not 

 matter what the spacing in the ocular micrometer may be, except 



that the lines must be at equal 

 .-- Eyei*rw\ distances from each other. As a 



oj the Ocular matter of fact, the ocular 



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 O 



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 wilh Society Screw 



m- 

 crometer is generally ruled in 

 tenths of a millimeter, but this 

 ruling is more or less magnified by 

 the lens of the ocular. 



Place the stage micrometer up- 

 on the stage and the ocular mi- 

 crometer in the tube, and arrange 

 the two sets of rulings so that the 

 first line in the ocular micrometer 

 will coincide with the first line of 

 the stage micrometer, and then 

 find the value of one space in the 

 ocular micrometer. The method 

 of finding this value is shown in 

 the following case in which the 

 tube length was 160 mm., the 

 ocular a Zeiss ocular micrometer 2, 

 and the objective a Leitz 3. In the 

 ocular micrometer, ninety-eight 

 spaces covered just fifteen of the 

 larger spaces of the stage microm- 

 eter. Since the stage micrometer 

 is ruled in tenths and one- 

 hundredths of a millimeter, the 



fifteen spaces equal 1.5mm., or 1,500/z. 1 Then 98 spaces of the 

 ocular micrometer equal 1,500 //; and one space in the ocular equals 

 -grV of 1,500 /z, or 15.3 /-i. This value being determined, there is no 

 further use for the stage micrometer. To measure the diameter of 



1 One millimeter = 1,000 M- The Greek letter M is an abbreviation for fj.iK.p6v, or micron. 



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FIG. 103. Tube length 



