GENERAL DIRECTIONS xiii 



almost invariably make the grave mistake of getting an object in focus, and then 

 examining it without any further change of focus, with the result that they do not 

 see all parts of the object, nor get a true idea of the relation in space of the parts. 

 The practiced microscopist never takes his hand from the fine adjustment screw 

 but continually changes the focus as he looks. The student should at once form 

 a habit of doing likewise. 



7. Moving the slide. As the image in the microscope is reversed, the slide 

 must be moved in the opposite direction from that in which it is desired to move 

 the image. This will soon become a habit. In moving a slide, do not put both 

 hands upon it but grasp it by the edges between the thumb and index ringer of 

 one hand. This leaves the other hand free to shift the focusing screw. 



8. Miscellaneous directions: 



a) If the image is dim or indistinct, or if the field rolls, or if the high power 

 cannot be focused, then in all probability the lens is dirty or wet. Clean it 

 with an old, soft handkerchief. If after cleaning the lens the high power will 

 not focus, then the material under examination is too thick and must be made 

 thinner. In case of any trouble with the microscope, don't tamper with the 

 instrument, but call the assistant. 



b) If images of buildings, etc., appear in the field, they may be obliterated 

 by using the concave surface of the mirror, or by lowering the condenser. 



c) In working with artificial light, use the concave surface of the mirror. 



d) Round black rings in the field are air bubbles under the cover glass. 



e) If the fine adjustment turns without producing any effect upon the tube, 

 it has come to the upper limit of its range and must be screwed down. If it will 

 not turn at all, it has come to the lower limit of its range and must be screwed up. 



/) Keep the microscope clean and free from dust. Do not let it stand in the 

 sunlight. Do not use sunlight for illumination in looking through the microscope. 



g) Keep both eyes open when looking through the microscope. If you find 

 this difficult, try placing an oblong of stiff paper around the top of the microscope, 

 so that the unused eye will not see objects. 



9. The magnification of the low power is about 50; of the high power, 500. 



KEEP THE LENSES CLEAN 



ADJUST THE LIGHT FOR EVERY OBJECT 



ADJUST THE FOCUS CONTINUALLY WHILE YOU LOOK 



