94 The Microscope (chap. 9) 



ocular eyepieces. Use a good grade of lens paper and a fine camel hair 

 brush. 



If glasses are worn, protect them from scratching by mounting a 

 rubber band aroiurd the top of the ocular. (Fingers of old rubber gloves 

 can be cut to fit the oculars.) 



If, instead of a mechanical stage, clips are present on a fixed stage, 

 place one clip over one end of the slide. Then with two fingers of one 

 hand controlling the loose end of the slide, move the slide for examin- 

 ing, while manipulating the fine adjustment with the other hand. 

 Individual preferences will determine which hand to use for which 

 motion. With a mechanical stage the right hand has to control the knobs 

 and the left hand the fine adjustment. 



If it is convenient to have a pointer in the eyepiece, unscrew and 

 remove the top lens of the ocular eyepiece. Inside, about halfway down 

 its tube is a circular shelf. Place a small drop of Permount (or other 

 quick-drying mountant) on this shelf and, with small forceps, place an 

 eyelash in this drop. Arrange the eyelash to lie flat and project a little 

 short of center of the hole formed by the circular shelf. Screw lens back 

 in place. 



When carrying a microscope, carry it upright, preferably with both 

 hands. Never tilt it; the ocular eyepiece can fall oiu. If using a micro- 

 scope for checking staining effects, or any wet mounts, place a thin piece 

 of glass on the stage. A lantern-slide cover glass {?>\ x 4 inch) is usually 

 available and is an ideal size for most microscope stages. Clean it after 

 use to prevent contamination of future slides or material. 



Measuring Devices Used on a Microscope 



Reading a Vernier 



Most mechanical stages are equipped with a vernier — a device for the 

 purpose of relocating the same spot previously examined on a slide. 

 Two numerical scales run side by side, a long one constructed on a 

 millimeter scale and a short one constructed on a scale of nine milli- 

 meters divided into ten equal divisions. When the area of reference on 

 the slide is centered in the objective, read the vernier. Check the point 

 of coincidence of the zero of the short scale against the long scale. Read 

 the lower whole figure on the latter, to the left of the zero on the short 

 scale. This determines the whole number, the number to the left of 

 the decimal point in the final reading (21. of the long scale in Fig. 22). 

 Exception: If the zero of the short scale coincides exactly with a whole 



