on the paper, the magnification would be 2500. If 18.6 

 on the rule are contained within three spaces on the 

 paper, the magnification would be 620 times. 



To Measure the Size of an Object. One of 

 the most valuable possibilities of the microscope is to be 

 able to accurately measure the actual size of a minute 

 object. Computations may be made in inches or milli- 

 meters by figuring 25.4 mm. equal to i inch. It may 

 be done by several methods, either of the following 

 being generally employed : 



The first of these gives satisfactory results on 

 coarser objects and wherever the most accurate results 

 are not required, although it is somewhat inconvenient. 

 The requisites are : 



A camera lucida. 

 A stage micrometer. 



The object is placed upon the stage and after 

 focusing, the camera lucida is attached and the instru- 

 ment set up exactly as for drawing. On the drawing 

 paper the outlines of object, or those portions which are 

 to be measured, are marked. Without in the least dis- 

 turbing any of the conditions of tube length or distance 

 from the paper, remove the object and replace it by the 

 stage micrometer, focusing only with the fine adjust- 

 ment and, it may be added, there should be very little 

 variation in thickness between the two slides. Move 



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