40 



THE MICROSCOPIST. 



A, Fig. 11, represents a brass ring, one-thirtieth of an inch 

 thick, whose inner diameter is about two-fifths of an inch. 

 Having dissolved a globule of quicksilver in one part nitric 

 acid and ten parts water, he rubbed with it the inner surface 



of the ring, which became silvered ; having wiped it dry, he 

 put a drop of quicksilver within it, which, when pressed with 

 the finger, adhered to the ring, and formed a convex speculum. 

 When the ring was taken up carefully, and laid on the margin 

 of the cylinder, B, the mercury sank down, and formed a 

 concave reflecting speculum. The cylinder, B, is supported by 

 a pillar, which is attached to the foot, D. The stage, Gr, is 

 for holding the object, and is adjusted to the focus by the screw 

 atC. 



