III. NOTES AXD DRAWINGS. 



1. Drawings should b'e made of every object studied; this is 

 necessary not only as a record of what has been seen, but also as 

 an aid to accurate observation. In general make outline drawings 

 only. Use hard pencils (/J.H-6H ), with very sharp points, and make 

 the drawings large enough so that all details can be represented with- 

 out confusion. Where certain structures occur in large numbers 

 it is sufficient to represent them in only a part of the drawing. 

 Label all important structures by means of reference lines and 

 marginal words. 



2. To draw to scale : Place paper at base of microscope and en- 

 deavor to trace outlines as seen with left eye while seeing point of 

 pencil at same time with right eye. The pencil point must appear 

 to coincide with the part of the object being drawn. Do not move 

 the eyes. 



3. To make a scale : Focus upon the lines drawn one-tenth 

 and one-hundredth of a millimeter apart upon a stage micrometer. 

 With a camera lucida draw several of the lines upon a card. Make 

 such a scale for each combination of lenses. Carefully label the 

 card with the lenses used and lay it away for future use. 



IV. EXAMINATION OF COMMON OBJECTS. 



1. Put a few fibres of wool, cotton, linen and silk in a drop of 

 water on a slide, cover with cover glass and examine first under a 

 low power, then under a high one. How do the fibres differ? 

 Sketch one of each and label them. 



2. Examine a drop of oil emulsion (oil suspended in water) and 

 notice peculiar effects of refraction when lenses are focused upon 

 different portions of a drop. 



3. Examine bubbles of air in water. These may be obtained by 

 running in water under a cover glass supported at one side by a 

 bit of paper and then tapping on the cover glass with a needle. 

 What differences can you see between these and oil drops? 



