280 PRACTICAL MICROSCOPY. 



opposite and equidistant from the centre, two circular 

 plates or discs, one inch in diameter, are set, their surfaces 

 flush with that of the large plate. Pivots from the two 

 discs project through the plate, and each carries upon the 



FIG. 233. 



lower side of the plate a toothed wheel. A hollow sleeve, 

 rotating free upon the stem of the table, carries a third 

 and larger wheel, which gears into the two others, and 

 thereby gives rotation to the discs in the top of the plate. 



Near the opposite edges of the two discs, the angular 

 jaws which hold opposite corners of the slide are pivoted 

 (as in Cox's and other forms of tables), and it will be seen 

 that by giving rotation to the central wheel, under the 

 plate, the jaws may be made to approach or recede at 

 pleasure. 



A coiled steel spring, concealed within the hollow 

 sleeve, serves to close the jaws, while the single motion 

 of a milled head upon the sleeve opens them to their full 

 extent. 



It may be also seen that although the jaws do not 

 approach in a straight line, yet, when properly adjusted, a 

 line joining the pivots of the jaws will cut the centre of 

 the plate, whatever the position of the jaws ; and they 

 being always equidistant from the centre, it follows that 



