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 were assumed to be invisible under the two inch. 

 Next, the pupil was required to adjust the object glass 

 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 T 

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

 slide, I care not how srnall nor how close the stride, and 

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

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

 the clot 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- 



