The Stage., 21 



2. The Jackson form of foot, as shown to instrument 

 on page 29. 



3. The flat tripod and upright pillars, as shown to instru- 

 ment on page 34. 



4. The Continental or horseshoe form. 



THE STAGE. 



It will be noted, on reference to the typical instruments 

 shown in this book, that the stage of the instrument on 

 page 17, on which the object is placed, is perfectly plain, 

 while those on pages 29, 31, etc., have screws, by means of 

 which plates move in dovetailed grooves one over the other 

 in rectangular directions, carrying the object with them. 

 In a first-class microscope it is well to choose ah instru- 

 ment having this convenience in fact, there is no means 

 so suitable for systematically examining an object as is 

 afforded by it. In addition to these mechanical movements, 

 if a sliding bar be fitted to slide on the top plate the con- 

 venience is greater. For plain stages beyond the springs 

 nothing is really necessary, and it is surprising how with a 

 little education the fingers will do the work of the mechanical 

 screws, so that the object may be carefully examined under 

 high powers. A sliding movement or some form of carrier 

 on a plain stage is preferred by some. 



A very great convenience to the mechanical stage is the 

 rotation, and this in a best instrument should be con- 

 centric ; some stages are fitted to rotate by rackwork, but 

 this is rarely necessary : it is often found convenient for 

 preventing the stage from rotating accidentally, especially in 

 photography, and should always have the pinion wheel so 

 fitted that it may be disengaged from the rack and replaced 

 instantly. Centring screws to the concentric rotating 

 stage, by means of which the rotation of the stage may be 

 made true with any objective, will be found a useful 

 addition. Divisions to the rotation of stages are not very 

 advantageous for ordinary purposes, but for geological work 



2 



