1891.] MICKOSCOPICAL JOURNAL. 159 



polariscope in the draw tube where there is no working distance for it 

 with Jow powers. 



The collar is the ornamental ring or projection at the upper end of 

 the chaw tube, or of the body when there is no chaw tube. It is unim- 

 portant to the pharmacist. 



The nose piece is the portion at the lower end of the body. It is 

 provided with a female screw, into which the objective is fastened. By 

 all means purchase a microscope with what is known as the "society 

 screw," so that any ordinary objective can befitted to it. I have found 

 that the English thread in the " society screw " is not quite the same as 

 the American, and I was obliged to get an adapter for the use of 

 English objectives on an American stand. This nosepiece has nothing 

 to do with the double, triple, and quadruple nose pieces, which are ac- 

 cessories, and not a part of the stand. 



The stage is of importance. The best for the use of pharmacists are 

 made of glass, so that they are not atlected by liquids or chemicals It 

 is an item to have a thin stage which admits of oblique illumination in 

 the examination of crystals. The expensive mechanical stages are verv 

 convenient, but not essential for the use of a drug clerk. 



The sub-stage must be so arranged that it will admit of the use of 

 sub-stage condenser, polariscope, etc. It is hardly worth while for a 

 pharmacist who expects to do much work to purchase a stand without 

 a sub-stage. 



The diaphragm is a contrivance for regulating the volume of light 

 which is admitted to the object. When a sub-stage is present, the dia- 

 phragm is adjusted to it ; otherwise it is attached to the stage in place 

 of the sub-stage. 



The mirror bar and its arrangement is plainly shown in the illustra- 

 tion. All modern microscope stands have the mirror bar so attached 

 that the mirror can be raised above the stage for the illumination of 

 opaque objects. This is a great convenience for the pharmacist who has 

 many substances to examine by reflected light. It is best to have a 

 mirror bar which can be lengthened or shortened as may be required. 



The mirror, if single, must be a concave one. Where there are two, 

 one is plain and the other concave. As far as the plain mirror is con- 

 cerned, the size does not make much difference, but the larger the con- 

 cave mirror the better. Pharmacists can use any mirror adapted to 

 ordinary work. 



The clips are for holding the slide in position. The ones which can 

 be removed are preferable for a pharmacist who occasionally has liquids 

 to examine, when the clips are in the way unless removed. 



The coarse adjustment is found on all instruments. The rack and 

 pinion arrangement is the best, and is the one used on the better class 

 of instruments. 



The Jine adjustment or micrometcr-scre~u.' is also a feature of the 

 better instruments, and should be present on every one owned by a 

 pharmacist who intends to do much work. It is much more convenient 

 to have the fine adjustment near the coarse one. By all means avoid the 

 instruments with the fine adjustment on the body near the nose piece. 

 They are inconvenient, and the use of them has a tendency to vibrate 

 the body of the instrument. 



As stated above, the ocular, or eye piece, and the objective do not 



