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DATED: 1878

SIGNED: 'Powell & Lealand, 170 Euston Road, London' and also dated '1878'

The mount for the Powell & Lealand No 1 is focused by rack and pinion. As shown in these images, controls on the mount itself include a crown gear mechanism to control rotation, and individual centering controls for X and Y directions.

It should be noted that the substage of this instrument is not equipped with a substage fine focus mechanism(shown on a later model, below), as these were not included until 1882.

subst engrlater P & L substShown here to the left is an engraving from Carpenter's book showing an engraving of the slightly later P & L substage from 1882. To the right, courtesy of Allan Wissner, are images of the later substage, showing the fine focus mechanism, which utilizes a tiny cone at the end of a screw to adjust the substage fine focus. This type of adjustment was used for focusing the main stage in Powell & Lealands massive stand made for the RMS, and also the fine focus of the main optical tube in the P & L 'New' Microscope of 1843. Although this mechanism was abandoned for focusing the main fine focus because of problems with wear, it apparently was still felt to be a sound method of fine adjustment to the substage for the latest and most sophisticated P & L No 1. This method of substage fine adjustment continued to be used on the P & L No 1 substage into the 20th century.

The authors are grateful to Allan Wissner for his kindness in photographing the substage assembly of his P & L No 1 and allowing us to use his images here.