ISO THE HISTOKY AND DEVELOPMENT OF THE MICEOSCOPE 



but in practice they are superfluous in the most complete instrument 

 beyond those 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 an 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 

 convenient 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 those 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 

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

 milled head below the stage. The lateral movement is produced by 

 two endless screws engaging in worm-wheels fixed to smooth rollers. 

 The lower edge of the slide rests on these, and is kept in gentle 

 apposition with them during traverse by a third smooth roller at the 

 free end of a curved spring as shown in the figure. This is readily 

 turned aside when changing the object. In its most recent form we 

 have used this stage with comfort and pleasure. 



Another of these stages, made by Baker from designs by Mr. 

 Allen, is shown in fig. 141, which in its latest form is so arranged 

 that the width of space between the rest and the spring clip can be 



