MEASUREMENT UNDER THE MICROSCOPE. 



can be obtained in the laboratory. This is an actual scale on glass 

 divided into fractions of a millimetre ( T &o) or fractions of an inch 

 ( y i_ an d ToVo)- With the ocular micrometer in the eye-piece focus the 

 divisions of the stage micrometer. 



Using the same eye-piece 

 and the same length of tube, 

 determine for each of your 

 objectives the number of 

 divisions of the stage mi- 

 crometer which equal one 

 division of the eye - piece 

 scale, and note the results 

 as follows : One division 

 of the scale in Oc. 2 with 

 Obj. 3 is equal to say 15 

 divisions of the stage scale 

 (^ mm) = o-15 mm , and with 

 Obj. 6 equals 3^ stage di- 

 visions = 0'0325 mm . The 

 same may be done with a 

 stage scale giving fractions 

 of an inch. The ocular 

 scale is now standardised 

 for those particular optical 

 combinations. For example, 

 to measure the diameter of 

 a red-blood corpuscle sub- 

 stitute a dried film of 

 human blood for the stage- 

 scale and using Obj. 6 find 

 how many red corpuscles 

 in a row fill one division of 

 the ocular scale. Assuming 



that it takes four, the dia- FIG. 3. Measurement, using both eyes. 



meter of one corpuscle is R right, and L left eye. M Microscope. SM 



0-0325 mm divided bv 4= Stage micrometer. S Scale of inches. C Com- 

 J . parison of the two images in the brain. It is presumed 



0*008 mm (Sp). Ihe metric thafc tne magnification is such as to produce a retinal 

 standard of microscopical image in the left eye equalling that in the right eye. 

 measurement is the micron 

 0'001 mm designated by the Greek JUL. 



In the absence of an eye-piece micrometer, proceed as follows : Look 

 through the microscope at the stagescale with the left eye, at the same 



