ADVANCED MANIPULATION. 



Dry Adjustable Objectives. The information 

 which has thus far been given on the manipulation of 

 the microscope may be termed initiatory, as it is sup- 

 posed (at any rate hoped) to have disclosed some 

 new principles. These are comparatively simple, and 

 with a moderate amount of attention, are easily 

 acquired. It is the intention now to speak of some- 

 thing more complex and to give instruction in the 

 use of higher grade adjustable and immersion objec- 

 tives. The difficulty of doing this increases with 

 each step of advance, and whether it can be over- 

 come by means of written words, is, perhaps, an open 

 question. However, the writer is certain that if the 

 following instructions are faithfully adhered to, satis- 

 factory results will be gained. The highest^ attain- 

 ment must of necessity be the result of perseverance 

 and knowledge of the various properties of an objec- 

 tive, which are given in preceding pages. 



It is assumed that a dry objective is used, say a |- 

 140 degrees or ^ 135 degrees, and provided with 

 screw-collar adjustment for cover-glass thickness ; it 

 is further assumed that in the first, the variation 



