Ch. IV] EXPERIMENTS FOR INTERPRETATION 125 



With the compound microscope it soon becomes as easy to move 

 the slide in the right direction to see a desired part as it is to make the 

 proper motions when examining an object with the naked eye, al- 

 though the motions are directly opposite in the two cases. Indeed 

 so natural does it become for the worker with the compound micro- 

 scope to make the proper motions for the object giving the inverted 

 image, that if he uses a compound microscope with an erecting prism 

 he almost invariably moves the preparation in the wrong direction 

 (§ 149a). With the simple microscope, however, it seems like naked- 

 eye observation and there is never any difficulty. 



This goes to show that by experience it is as easy to interpret 

 inverted as erect images. This is further illustrated by the printer 

 who learns to read type without difficulty, although it is a great puzzle 

 to one who has only learned to read the appearances after the type 

 has been printed on paper. 



§ 218. Summary for proper interpretation. — To summarize this 

 chapter and leave with the beginning student the result of the experi- 

 ence of many eminent workers: 



(1) Get all the information possible with the unaided eye. See 

 the whole object and all sides of it, so far as possible. 



(2) Examine the preparation with a simple microscope in the 

 same thorough way for additional detail. 



(3) Use a low power of the compound microscope. 



(4) Use a higher power. 



(5) Make sure that the mirror is in the best position to give the most 

 favorable light. Vary the aperture by opening and closing the iris dia- 

 phragm to find the aperture which gives the clearest image in each case. 



(6) Shade the top of the stage of the microscope to cut off the 

 light from above and thus avoid confusion from that source. 



(7) Use the highest power available and applicable. In this way 

 one sees the object as a whole and progressively more and more detail-. 



(8) If one has the apparatus it is a good plan to examine specimens 

 w T ith a binocular microscope to gain the best notion possible of the 

 relative position of parts of the specimen. 



(9) Use the dark-ground illuminator (§ 210), the spectroscope, and 

 polariscope (Ch. VIII). 



