748 



APPENDIX. 



centrically with optic axis of microscope. c a plate of 

 polished glass let in and secured to upper surface of B. 

 D D, a v spring attached to outer edge of the plate B and 

 rotating with it, having at the outer extremities projecting 

 " ivory " points d d. e the object-carrier, consisting of 

 another plate of polished glass, mounted in brass frame, 



Fig. 360.— Crouch') Concentric Stage. Scali; J. 



having an attachment for holding the object. The plate 

 e projecting slightly on the lower surface from the brass 

 frame is kept in contact with the circular plate c (also 

 slightly projecting above b), the two glass surfaces being 

 in contact, and kept so by the pressure of the "ivory 

 points" dd; thus securing a beautifully smooth and 

 delicate — though firm — adjustment, which admits of 

 an object being found with extreme facility under the 

 highest powers. It is particularly adapted for the ex- 

 amination of objects in fluid of any kind, the adjustments 

 not being subject to oxidation ; any minute object may 

 very readily be found, and the slightest change in the 

 field, is easily effected ; there is no slipping back or recoil 



