288 HOW TO SEE WITH THE MICROSCOPE. 



if but a sixth, then you will need the " D" solid, the 

 one-half inch. Try now and display the striae on the 

 little shell ; remember that they are at best but very 

 thin and faint. Nevertheless, if there has been suffi- 

 cient practice with the " lesser illumination " previously 

 mentioned, there ought to be now but little trouble in 

 recognizing the lines. When once a good view has- 

 been obtained, the observer will be astonished by a 

 little experimenting, to find how far the lamp wick 

 can be turned down just allowing the flame to peep 

 out of the cone and still retain nice views of the 

 striae. 



This entire position, including that of observer , 

 stand, mirror, and condenser, we have tried to illus- 

 trate in the cut on page 289, the diagonal pose of the 

 condenser we have intentionally exaggerated. It is 

 probable, too, that the student may find it necessary to 

 make some slight changes to suit the tools he may have 

 in hand. Let him keep this fact prominent, to wit,, 

 although the condenser will give more light than the 

 illumination first recommended, nevertheless there 

 must be no more light used than is absolutely required 

 to see the object without difficulty as respects illumina- 

 tion. If it be desirable at any given time to employ a 

 higher ocular, always turn up the wick of the lamp ; a 

 slight turn will be found quite sufficient, and while on 

 this subject let me say that nine out of ten microscop- 

 ists use far too much light. They seem to be impressed 

 with the idea that unless the object is bedazzled in a 

 flood of light that it is not well shown. All this is in 



