124 EXPERIMENTS FOR INTERPRETATION [Ch. IV 



mistaken for lymphatic vessels — Beale, 288) ; fibers of cotton, linen, 

 and silk (textile fibers accidentally present have been considered 

 nerve fibers, etc.); the scales of butterflies and moths, especially the 

 common clothes moths; the dust swept from carpeted and wood floors; 

 tea leaves and coffee grounds; dust found in living rooms and places 

 not frequently dusted (in the last will be found a regular museum of 

 objects). 



§ 216. Wire gauze experiment. — For a very striking illustration 

 of the need of care in interpretation with naked eye observation, take 

 two pieces of wire gauze such as is used for milk strainers or some 

 slightly coarser. Place these over each other and look through them 

 toward the light. Where there is but a single layer the weave is 

 evident, but where the two pieces overlap the appearance is very 

 puzzling, and changes constantly as one piece is rotated, bringing the 

 threads and meshes at an angle. One could hardly believe that the 

 structure is so simple when looking through two layers of the gauze. 



If it is necessary then to see all sides of an ordinary gross object, 

 to observe it in various positions and with varying illumination and 

 under various conditions of temperature, moisture, and in single as 

 well as multiple layers to obtain a fairly accurate and satisfactory 

 knowledge of it, so much the more is it necessary to be satisfied with 

 the interpretation of appearances under the microscope only after 

 applying every means of investigation at command. Even then 

 only such details of the image w T ill be noted and understood as the 

 brain behind the eye has been trained to appreciate. 



§ 216a. Experiment with wire gauze. — For this very striking, naked-eye 

 experiment with the wire gauze the author is indebted to a suggestion from Dr. 

 Chamot. 



§ 217. Inversion of the microscopic image. — As all the images 

 produced by the modern compound microscope are inverted unless 

 they are erected by a special arrangement of prisms, one must learn 

 to interpret the appearances in an inverted image with the same 

 certainty as in erect images seen by the naked eye or through the simple 

 microscope. It may be remarked in passing that with the compound 

 microscope the image is actually erect on the retina of the eye (fig. 



3> 2 °)- 



