284 HOW TO SEE WITH THE MICROSCOPE. 



Watch, when the flame flickers, for that little band of 

 light, and when you catch it remark the wondrous deli- 

 cacy of its tone. Note, too, how the flickering of the 

 flame bathes the field with minute differences in tone, 

 things are almost alive. Compare what you now see 

 with anything that you saw a month ago. Has not your 

 time been well expended? 



When the student has arrived at a position that will 

 enable him to fully appreciate what I am now writing, 

 he is safe. No matter should he have been accustomed 

 to the use of low apertures from childhood, he can never 

 be forced to return to his first love, nor will he have 

 trouble in following me to the very end. 



Should the learner unfortunately find that in this les- 

 son he cannot see things as described, and presuming 

 that the objective is competent for the work, then it 

 must occur that there is either trouble with the manipu- 

 lations, or his eye is not sufficiently trained for the work 

 in hand. Hence he cannot get the mirror far enough 

 downwards; i. e., he is compelled, in order to see the 

 lines at all, to use light of too much obliquity. There 

 is but one remedy (if he is sure as to the capacity of his 

 objective, which he ought, perforce of the preceding 

 lesson to demonstrate), to wit: Practice until the end 

 shall be arrived at. 



This effect, due to the lesser illumination, has, as the 

 reader will remember, received our attention on a fore- 

 going page. It may be advisable that he review what 

 has been said, and thus combine theory with practice. 



Lesson Twelfth. We are now to deal with the more 



