240 HOW TO SEE WITH THE MICROSCOPE. 



exhibited by the object selected. Our reason for mak- 

 ing at this time the particular selection was this : When 

 the objective was in perfect adjustment, the striae were 

 admirably well seen when the inch ocular was employed,, 

 but w r ere assumed to be invisible under the two inch. 

 Next, the pupil was required to adjust the object glas& 

 using the two-inch ocular only, acting, of course, under 

 the general instructions he had received. This done he 

 was to apply the higher eye-piece and learn of his suc- 

 cess, practically. Our friend went at his task manfully, 

 and fought that slide of diatoms three hours or more 

 daily for more than a full week, constantly improving 

 in its manipulations. Then it occurred that, getting 

 somewhat weary of his protracted efforts over one and 

 the same slide, he began to beg for a change to do some- 

 thing else. Nevertheless, he was put off time alter 

 time, until nearly at the close of a long evening's work 

 he jumped up from his table, and running towards me, 

 his eyes beaming with joy, exclaimed, " I have it! I 

 see it! It's all plain sailing now!" "Well," said I> 

 "what is it?" He replied, " I can see any shell on that 

 slide, I care not how small nor how close the striae, and 

 as well with the two-inch ocular as with any other; and 

 more than that, I can put the correction collar right 011 

 the dot without humming or hawing, and do it every 

 time." To this we responded: " You have now solved 

 your problem, and are ready to tackle another mount 

 at our next sitting. 



Now, reader, here is a practical case in point: My 

 pupil had not only been improving himself in the "hand- 



