MICROSCOPIC OBJECTS. 201 



required to work easily. It will be remarked that, 

 however heavy the body may be, it can always be 

 balanced by sliding it in its containing tube ; and when it 

 is quite vertical, and its whole weight, aggravated in 

 effect by the lever of the neck, strains the cradle-joint, 

 the body will be retained in its position by the projection 

 at e, on which the neck ^vill rest, m is a sliding-rod of 

 wood ; it passes into the pillar p, and is retained in its 

 position by the pinching- screw which is attached to the 

 cap n. The screw acts upon a spring adapted to the 

 shape of the rod in the inside of the wooden tube or pipe, 

 which is perforated from end to end. The pillar is 

 w^edged and glued or screwed into the wooden farciform 

 tripod frame q q, which may be made solid or in two 

 pieces ; it can also be made of pewter (painted in oil in 

 imitation of wood). Tliis tripod frame has its inner 

 contour circular, but its two prongs project straight a 

 little way beyond the centre of gravity of the body. 

 Three screws, r, r, r, are fixed into the extremities of 

 the stand, made of ivory or hard wood ; holes are drilled 

 into the ends of them, and pieces of black lead or French 

 chalk are inserted (as in the patent pocket-pencils). See 

 the detached one. If the reader should want to know 

 the use of these pencils, I beg to inform him that the 

 instrument is to be placed on a piece of good Irish slate, 

 or a pohshed plate of copper, or one of glass ; (the first 

 gives the most friction, the latter the least;) and that 

 grasping the piUar at the bottom he is to slide the 

 instrument about thereupon at his pleasure, over the 



