12 ZOOLOGY DTBECTIONS 



3. Proper way to carry a microscope. In carrying a mi- 

 croscope, it slionld be lifted by tbe arm and held in an approxi- 

 mately upright position to prevent the ocular from dropping out. 



4. Lenses. The lenses consist of (a) the ocular or upper 

 lens, (b) a low power objective^ the shorter of the two objectives 

 and (c) a high power objective, the longer of the two objectives. 

 Before and after using see that the lenses are clean. Use lens 

 paper for cleaning them. Do not use cloth. The low power 

 objective is much more effective than the other for all ordinary 

 work. Do not use the high power objective when you can make 

 out the desired points with the low power. In using the high 

 power, find the object under the low power first, move the part 

 you desire to examine with the high power to the exact center of 

 the field of the low power, and then if the lenses are "parfocal" 

 swing the high power objective into place. In case you find the 

 two objectives are not directly interchangeable (=parfocal) 

 draw the tube of the microscope up by means of the coarse ad- 

 justment and then swing the high power objective into place. 

 Now with your eye at the side of microscope on a level with 

 the stage, lower the lens until it almost touches the coverglass. 

 With your eye at the ocular, focus upward until the object comes 

 into view. 



5. Focusing. The working distance of the fine adjustment 

 is short and it is therefore always necessary to get the approxi- 

 mate focus with the coarse adjustment before using the fine. In 

 using the coarse adjustment ALWAYS FOCUS UPWARD. 

 This relieves the possibility of ruining the lens or the slide. 



6. Light. The proper adjustment of the light is essential. 

 It is accomplished by giving the mirror the proper tilt and by 

 changing the size of the opening in the stage. In some of the 

 instruments there is a so-called iris diaphragm for this purpose, 

 below the stage of the microscope. Study the operation of the 

 mirror and of the diaphragm. Then with the eye at the ocular 

 practice adjusting the mirror so as to secure a perfectly uniform 

 illumination of the field of the miscroscope. 



