THE MTCEORCOPE 15 



Before inserting the ocular micrometer into the tube of the mi- 

 croscope look through it toward the light and adjust the draw- 

 tube until the lines and figures in the field of the ocular becomes 

 most distinctly observable. 



These lines are always the same distance apart regardless of 

 the power of the ohjective used but since the size of the image to 

 be measured varies with the objective used it becomes necessary 

 to find the value of the ocular divisions for the different objec- 

 tives. When used with a low power (Spencer Lens Co. 16 mm.) 

 objective a single one of the smallest divisions of the ocular 

 scale has the value of 0.0078 mm. AVith the high power (Spencer 

 Lens Co. 4 mm.) objective each of the smallest ocular divisions 

 has the value of 0.0017 mm. 



To measure an object under the microscope find the number 

 of smallest micrometer units in the length (or other dimension) 

 of the image and multiply that number by the value, as given 

 above, of a single ocular unit for the objective you are using. 



REFERENCE 



Gage, Simon Henry, 1925. The Microscope, An Introduction 

 to Microscopic Methods and to Histology. Comstock 

 Publ. Co. 



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