300 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Watson's Mechanical and Rotating Stage. — Fig, 46 sliows an 

 improved form of stage by Mr. Watson, with the mechauical move- 

 ments applied to and wholly controlled on the surface and within the 

 circumference. It will be remembered that at pp. 117-18 we figured 

 and described Tolles's mechanical stage, embodying similar move- 

 ments. In the Watson stage, however, the lower plate or bar, travelling 

 vertically, is sunk below the surface of the stage and moves in a dove- 

 tailed gi-oove ploughed out of the rotating plate, and carries a pinion 

 whose teeth gear into a rack cut into or attached to one side of this 



Fig. 46. 



groove. By turning the milled head fixed to this pinion — the upper 

 one in the figure — the plate carrying it moves in a vertical direction. 

 To this bar is attached another at right angles, with a similar groove 

 ploughed out, in which works a second plate having teeth cut upon its 

 lower edge gearing into those of a second (hollow) pinion placed on 

 the first, and, by means of a tube fitting the axis of the latter, turning 

 independently upon it by the lower milled head shown. Thus, as 

 with the ordinary " Tyrrell " pinion movement, by turning either of 

 the milled heads separately, rectangular motion can be obtained — or, 

 by turning them both together, diagonal motion. 



To the plate or bar, traversing horizontally, is attached the top 

 plate (upon which the object slide is placed), the thickness of which 



