180 THE HISTORY AND DEVELOPMENT OF THE MICROSCOPE 

 i.ut in practice they ;HT superfluous in the most complete instrument 



beyond t hose indicated. 



There is a simple form of attachable mechanical stage now em- 

 ployed by many, and we think with advantage, when the cost of a 

 complete mechanical .stage must be forgone. This consists of a clip 

 to receive the object, made of glass or .brass, so arranged that the 

 friction shall be reduced to a minimum. 



Such .-in attachable stage can be made to work with remarkable 

 smoothness ; and since some persons have not sufficient delicacy of 

 touch to move so small and thin an object as a 3 X 1-inch slide upon 

 the stage with steadiness and precision, it is in favour of the super- 

 stage that it is larger, moves easily, and can be furnished with 

 cnii\ eiiient points of hold-fast for the hands, and consequently is 

 more manageable. Against its employment is the fact : 1st, that 

 the slide is clipped into a rigid position ; and 2ndly, that the aper- 

 ture is often too small to admit of the employment of the finger in 



FIG. 140. Swift's attachable mechanical stage (1894). 



moving the slide to assist in rapid focussing. But these are defects 

 which are rapidly disappearing. 



Amongst tlio.se that claim the attention of the microscopist is 



that of Messrs. Swift and Son, shown in fig. 140. It can be adapted 



to most microscopes; it is easily applied and removed, leaving the 



itage, if required, free. The up and down motion is effected by a 



milled head l>elo\\- the stage. Th.. lateral movement is produced by 



wo endlesi screws engaging in worm-wheels fixed to .smooth rollers. 



I'lie lower edge of the slide vests on these, and is kept in gentle 



apposition \\itl, them during traverse by a third smooth roller at the 



<-nd of a curved spring as shown in the figure. This is readily 



vh.-n changing the object. In its most recent form we 



; this stage with comforl and pleasure. 



?es, made by I'.aker from designs by Mr. 



Ill- uhich in its latest form is so arranged 



space between the cesi and the spring clip can be 



