306 HOW TO SEE WITH THE MICROSCOPE. 



; tera will answer a good purpose, and in the summer 

 time the student will find a plenty of these visitors, 

 and from such material many excellent mounts can be 

 prepared with little loss of time and at a slight ex- 

 pense. We recommend that the pupil become well 

 accustomed to handling insect scales before attempting 

 the miscellaneous examination of anything and every- 

 thing mounted dry that perchance may be directly at 

 hand. After considerable proficiency has been secured, 

 the student, may test his powers thus: Let him pro- 

 vide himself with a dry mounted trachea, say of a bee; 

 use the lowest ocular, select the strongest and most 

 vigorous part of the object where the coils are the 

 largest and the strongest, and adjust the glass as nicely 

 -as possible thereon. This done, choose one of the 

 longest continuous coils and see how far this can be 

 followed towards the smaller end. Now having arrived 

 at the limit, so that the coils can but just be perceived, 

 manipulate the adjustment; now if you succeed in get- 

 ting very much better definition,, the proof is before 

 you that you were in error at the commencement. 

 Make a note of the situation, and throwing the glass 

 intentionally out of adjustment again, repeat the ex- 

 periment until you shall be enabled to certainly make 

 the initial correction with tolerable certainty and accu- 

 racy. This is first-class practice, and will be of the 

 utmost value in general work over dry mounts. The 

 trachea, too, is a real good test object. The author has 

 worked ten hours at a sitting endeavoring to trace 

 these coils to the very last end, but has thus far met 

 with defeat. 



