56 



watching the field as the objective is brought down 

 toward the object, but is often followed by disastrous 

 results. Almost any person who has used the micro- 

 scope for any length of time is without question 

 aware that valuable preparations have been destroyed 

 in this way. 



How to Work. It is now supposed that the 

 instrument is ready for work. To start, it is well for 

 the beginner to provide a few prepared specimens, as 

 these will help him considerably if it is his intention, 

 as it should be, to prepare them later himself. What- 

 ever branch of study he is going to follow, a slide of 

 pleurosigma angulatum, dry, will be valuable to prac- 

 tice upon and to determine the quality of his higher 

 power objective. In this latter respect, however, the 

 writer would advise the beginner to guard against 

 expressing an opinion too soon. He knows of many 

 cases where the optician's claims were flatly denied, 

 when often a few words of advice by lettter or a few 

 minutes of intelligent manipulation would resolve the 

 diatom, and would thereafter do it so easily that it 

 became a wonder how it could possibly be avoided. 



For a low power objective, the proboscis of a blow- 

 fly is probably the most suitable and at the same time 

 most interesting object. Place this upon the stage, 

 and, after getting it as close as possible to the center 

 of the opening in it, focus by means of the coarse 

 adjustment. If only a portion of it can be seen and 

 if it is desired to see a larger surface, the length 

 of tube may be contracted by means of the draw-tube. 



