14 PRACTICAL TREATISE ON 



represented by fig. 10. It consists of an octagonal base of 

 wood, z, which supports a square pillar of brass, I k, having 

 a ball and socket joint at m. On the pillar, I k, an arm, d, 

 carrying the compound body a^aP', is made to slide up and 

 down, and above it another smaller arm, g, which has a screw 

 for tightening it at h; f is a long screw attached to the 

 arm, d, carrying the compound body, and when the arm g 

 is fixed by the screw h, the nut i will raise or depress 

 the compound body ; p is the stage, which is fixed to the 

 piUar by the arm n n and the nut o, a fish is laid on it 

 for examination ; r is a convex lens, for concentrating" on 

 the stage the rays of light from the candle, s, which was 

 placed on a stool, or on the ground, whilst the microscope 

 stood on the edge of a table; v is termed a leaden coffin, 

 for putting over the fish to keep it from moving. The 

 optical part of this microscope consisted of two convex lenses, 

 forming the eye-piece in the compound body, and of six 

 magnifiers, which could be screwed to the tube c. The 

 pillar, I k, was marked with the numbers 1, 2, 3, &c., to 

 show the respective distances of the magnifiers from the 

 object. There was no mirror to this microscope, but direct 

 light could be used when the body, by means of the ball and 

 socket-joint, was turned horizontally. A drawer, t, in the 

 stand, z, served to contain the magnifiers and other appa- 

 ratus. This instrument was subsequently much improved 

 upon by Mr. Culpeper and Mr. Scarlet, and will be pre- 

 sently described. 



In 1738, a new aera in microscopic science presented itself, 

 viz. : the invention, by Lieberkuhn,* of the solar microscope, 

 and of a concave silver speculum for viewing opaque objects, 

 which still bears his name, both of these instruments were 

 subsequently greatly improved upon by our countryman, 

 Mr. Cuff. The solar microscope, as invented by Lieberkuhn 

 could not be employed unless the sun's rays fell directly upon 

 a condensing lens, therefore its use was limited to a short 

 portion of the day. Cuff, however, applied a moveable 

 mirror to it, and made it more available for general use. 

 * Dr. Nathaniel Lieberkuhn of Berlin. 



