270 HOW TO SEE WITH THE MICROSCOPE. 



corrected to a greater extent than others. Whatever 

 may be the correction of a given object-glass, there 

 will be a corresponding tone to the field, and it's the 

 business of the learner not only to know the fact but 

 to be competent to recognize the characteristic appear- 

 ance presented not by the particular object viewed 

 alone, but by the entire field of view. And here again 

 comes some nice eye work. The artist can look at the 

 landscape and recognize the very "atmosphere" not 

 so the shepherd's boy. The former might talk until 

 dooms-day to the latter as to ' atmosphere." 



Now every good object-glass has an "atmosphere" 

 of its own, peculiar to itself, and depending on the 

 individual corrections of the glass. A moment's con- 

 templation of the situation teaches the difficulty attend- 

 ing any effort on the part of the author to make him- 

 self understood so as to be of service to the learner. 

 Nevertheless, the attempt shall be made. 



Lesson Sixth. Place the shell of rhomboides exactly 

 in the centre of the field, and adjust the object-glass. 

 Arrange the mirror with its radial bar, so as to illumi- 

 nate at about 45 or 50 from axis. Focussing sharply, 

 examine well your diatom as to color; the chances are 

 that both blue and red are to be observed. Select in 

 turn several shells and thus examine, and finally in- 

 spect all the objects on the mount before mentioned. 

 A little patient attention will teach you that there is 

 something apparently due to the blue that does not 

 attach to the red. For instance, the shells may have a 

 slight lavender tint; as soon as one can detect any- 



