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MAKER: Unknown but fits early Powell & Lealand Microscopes and the P & L No. 3.


c. MID-1/3rd 19th C.


Please Click On Any Picture for a Larger Version

plo plategonio on stage plateThis device is designed to hold a microscope slide at a compound angle. As shown to the left, the top half of the upper double-plate of my 1843 Powell & Lealand microscope stage slides off the piece under it. The goniometer stage attachment then slides on to take its place(right). The piece it slides onto can rotate as the bottom of it is a cylinder fitting into a sleeve on the rest of the stage. One of the dovetail edges of the goniometer attachment is sprung with a leaf spring, thus assuring good fit which is firm, but still easily moved or removed at will. The goniometer will also fit the later Powell & Lealand No 3 models. As noted, the goniometer can rotate horizontally when in place, as the top plate of the microscope stage is made to rotate.

The goniometer itself can adjust to tilt the slide in two axes. These are both calibrated in degrees. The knob on the front of the goniometer stage attachment tilts the slide holder right or left. The scale on the front sector is calibrated from 0 to 30 degrees tilting rightward and 0 to 30 degrees tilting leftward. The knob on the left side of the goniometer stage attachment tilts the slide holder toward or away from the microscope. The scale on that sector is calibrated from 0 to 50 degrees for tilting towards the microscope and from 0 to 30 degrees for tilting away from the the direction of the microscope. Both sectors are marked in single degrees, labeled every ten. There are knife-edge indicators on each one and are each controlled by a pinion acting on a sector. The support for the slide has two stage clips. This device then allows tilting in two axes, each calibrated on toothed sectors attached to the slide-holding piece. The finish is lacquered brass to the knobs and sectors, with the rest of blackened brass.

from quekett, 1848
The first use of a gimbaled stage, the precursor of the goniometer stage, has been attributed to Amici about 1842. The stage goniometer was apparently invented before 1845, as one that was adjustible and calibrated in the horizontal plane and could also tilt in one axis in a similar way to the one pictured on this page, was first described and illustrated by Leeson (Mem. Proc. Chem. Soc., 1845,3, 486-560). The same apparatus was also described in the first edition of Quekett's Treatise of 1848 (see Figure to the left). There it was referred to as an adjusting stage, to be used to position the crystal so its crystal face angles could be measured with a Leeson eyepiece goniometer. In that chapter, its use, with an eyepiece Leeson goniometer, in measuring interfacial crystal angles (not optical angles) is described in detail. Its main function is merely to position any of the different interfacial crystal axes of a crystal in a horizontal plane, to allow the angle of the axis to be measured by the (much more precise), Leeson eyepiece goniometer.

The Leeson eyepiece goniometer contains a double image prism (not a nicol prism). It is used without a polarizer or analyer. As the goniometer prism is rotated, the crystal faces eventually become parallel, and the angle beween them can be read on the scale. This is not the same instrument as a plain goniometer that has no prism. The use of a goniometer stage such as Leeson's or the one shown on this page should not be confused with the later and much more precise universal stagesused to determine the optical axes of crystals. The goniometer stage could have also been used for simpler tasks such as simply tilting a subject to view it at different angles, much the same as the simpler uncalibrated 'Stage Mineral Holder' of Beck.

This well-made device is in excellent mechanical condition. It operates quite smoothly. There is some mild spotting to the lacquer of the sectors and knobs.

The author is grateful for the suggestions and input of Dan Kile and Joe Zeligs regarding the content of this page.