THE POWELL & LEALAND IMPROVED LARGE FIRST CLASS MICROSCOPE

MAKER: POWELL & LEALAND

DATED: 1854

SIGNED ON THE ARM: Powell & Lealand, Seymour Place, Euston Square, London, and is dated 1854

AUTHOR: Jurriaan de Groot

Editor: Barry Sobel

The figure to the left shows the arm of the 1854 Powell & Lealand and the fine focus mechanism. This is what is known as a long lever fine focus mechanism. The mechanism takes advantage of a fulcrum point closer to the nosepiece which means that larger movements of the end of the lever acted upon by the fine focus knob, produce smaller changes at the nosepiece. Unlike in another example of this microscope dated 1858, the spring action is here provided by a brass leaf spring acting on the nose-piece instead of the helical coil spring which came into use later. The arm can be rotated sideways through more than 90 deg, with one stop aligning the body tube with the optical axis. It can be fixed into position by tightening a screw (visible behind the braces in the top image) which can be tightened with a Tommy-bar. The top image shows the arm attached to the limb, the middle image shows the arm as viewed from its underside, and the bottom figure shows the springs with the lever removed.

A. Attachment of arm to pillar
B. Fine adjustment dampening spring
C. Long lever upon which the end of the fine adjustment screw acts.
D. Pivot axle which acts as the fulcrum for the long lever
E. Nose-piece return leaf spring
F. Nose-piece with pre-RMS P & L 17 mm thread
G. Fine focus control