284 



CONTRIBUTIONS TO MICRO-MINERALOGY. 



is ordinarily fitted with a plain metal plate that rises flush with 

 the top of the axes of the stage, or this may be replaced with 

 another plate, which rests on three screws, and has an arm pro- 

 jecting from one side, by which heat may be communicated to 

 the centre of the stage, when a spirit-lamp is placed under it ; 

 the three points of support not allowing the heat to be com- 

 municated to the other metal work. These three plates have 

 apertures in their centres, with screw rings, so that they may be 

 fitted with circles of thin glass, when liquids are used. If a 

 movement is required beyond that afforded by the object slides 

 having free play in all directions, a circular plate of metal or 

 glass, about 1 inch less in diameter than the bottom plate of the 

 stage, with an inch aperture in the centre, may be used as sug- 

 gested by Professor Smith, motion being imparted by the ope- 

 rator's fingers, or a Tilley's, or any other form of mechanical 

 movement may be fitted within the ring of the stage. Of course, 

 in this instrument the object has to be placed with the thin 

 cover downwards. 



By removing the nut N, the stage has free movement 

 on its axes, and may be inclined to any angle, as is shown in 

 fig. 4, S. S. One axe is longer than the other, and is so 

 arranged that the graduated circle before mentioned may rotate 

 on it, and be clamped, when desired, by the nut N. An index- 



