Back Button





DATED: 1843

SIGNED ON THE ARM: 'Powell & Lealand, Makers, London' and also dated '1843'

Please Click On Any Picture for a Larger Version, where available

The images above illustrate the mechanism of the mechanical stage, with the images to the right and left of center showing the mechanism of the mechanical portion of the stage as viewed from its bottom, after it was detached from the main stage plate. It is of the type invented by Turrell, with concentric controls. This allows right-left(X-axis), forward/backward(Y-axis), or, when both knobs are turned simultaneously, diagonal motion.


The Y axis(forward/backward) motion is by rack and pinion, and the X-axis(right-left) motion is by a wormscrew-like device known as a 'constant lead cylindrical (or barrel) cam' acting on the 'follower', shown in detail to the left. The follower, is the part with a V-shaped point fitting in the spiral groove of the cam, and is attached to the bottom-most plate carrying the parts of the stage moving the slide. It is kept in contact with the cam by a bent-metal spring. This mechanism for the X-axis was apparently retained by Powell & Lealand for all Turrell type stages found in the future No 1, No 2, No 3 and No 4 models.

stage plateThe entire mechanical stage is held on a firm stage plate(long green arrow) by four screws. The screws pass through holes in the corners of the stage plate(short green arrows), from below.

slide restThe slide being studied is held in position between one fixed and one sliding 'bar'(left) on a sliding double-plate which sits on the top of the mechanical stage assembly.

fixed bar
The fixed bar is raised above the surface of the uppermost plate by a narrower piece of brass in the center of it. A removable brass insert fits in from the front of this fixed plate, filling in the spaces on either side of the central piece. This arrangement might allow the insertion of an accessory slide-holding piece when the inserted piece is removed. The brass spacer is not rectangular, and being angled and wider in back, only allows the insert to fit in from the front.


moving slide restAs can be seen in the image to the right, the moveable bar has a sprung pressure-plate to hold the slide in position against the fixed bar.

The entire top double-plate can be manually pushed forward or backward, and the fitting it slides on rotates.

P and L microscope mech stage The top plate of the double-plate is pushed upward by a spring mechanism of the same type used for the pressure plate of the moveable bar shown above. This sprung mechanism then forms a 'safety stage'. This helps to ensure that if an objective is accidentally racked down on to the slide while focusing, the top surface of the stage gives way, downward. The top part of the double-plate has four small rods, one near each corner, which fit through holes in the lower plate. These rods have round cap-like ends resembling nails, preventing the upper plate from coming off. Attached to the underside of the bottom plate, are two leaf springs. The tips of the rods are held upward by the far ends of these two leaf springs. These springs are attached by screws at their centers to the bottom plate so that their ends push upward on the rods coming down through the holes in the lower plate; the ends of the leaf springs(red arrows), then give way when downward pressure is applied to the stage, preventing damage to the slide and/or objective.

When the top double-plate assembly is slid backwards towards the limb, it reveals two holes on the plate beneath it which it slides on. The holes in this plate beneath the double-plate can receive stage-mounted accessories such as a stage forceps or stage-mounted bullseye condenser.

The sequence below illustrates how the parts are added on top to produce the final assembly.

seq 1 The controls of the mechanical stage act on a plate with a ring on top. This plate moves in dovetail guides.

seq 1dovetailsThe first part added on top of this plate is a rotating plate that has a round fitting on its bottom to slide down into the brass ring on top of the rest of the mechanism. Note the two holes with fittings on the bottom of the rotating plate to secure stage-mounting accessories like a stage forceps. After the rotating plate is in place, the next piece to be added is the sprung double-plate with a fixed slide rest. As shown to the right, it slides on via a sliding dovetail arrangement.

seq 1seq 1As shown to the left, the double plate dovetails on to the rotating plate by sliding on from the front. When it is slid past the midpoint, as shown to the right, the two holes for accessories on the plate beneath it are revealed.

seqseq Finally, the moveable slide rest, or bar, dovetails on to the sprung plate to complete the stage. Notice how thick this arrangement is(right).


P and L microscope mech stage