The following was extracted from the 1892 Bausch and Lomb catalog; it indicates that either the Model, Universal, or Professional stands could be converted to petrological instruments:

No. 570--PETROGRAPHICAL MICROSCOPE.

The rapidly increasing interest in microscopical work in geology which is manifested in all parts of: Americas, together with the difficulty and expense of importing instruments for this purpose from Europe seems warrant the construction of a fully equipped petrographical microscope at home.

The importance of supplying this want in the United States was suggested by Dr. George H. Williams, Associate Professor of Mineralogy and: Inorganic Geology in the Johns Hopkins University, Baltimore who has specified various points necessary to a microscope destined especially for rock-study, and who has approved the complete instrument as submitted to him for examination. It is believed that this microscope embodies the best features of the European instruments and that it is superior to any them now offered for the same price. The cut and description apply to the microscope as applied to our Model stand in which it is exceedingly compact and low priced; but we attach it as well to the Universal and Professional stands in which connection they are proportionally elaborate. The essential features of the Petrographical Microscope are as follows:

1--The lower Nicol (polarizer): is mounted in a cylindrical box beneath the stage to which it is held by a swinging arm so that it may be thrown: instantly to one side if desired. This polarizer may be vertically raised or depressed by rack and pinion movement, and is also capable of an axial revolution upon a graduated silvered circle. It is provided with a compound lens for securing converged polarized light, which may be removed at will.

2--The stage consists of our circular mechanical stage (No. 1054) provided with graduated scales to mark both of its rectangular movements. It is adapted for complete concentric revolution, and is provided with graduated and silvered circle and index reading to degrees.

3--The nose-piece is provided with a special adapter to which the objective may be screwed. Into this are made to slip four of the following accessories each mounted in a separate brass frame: a, Bertrand's lens for magnifying the interference figure: b, a quarter undulation-mica-plate: c, a quartz wedge: d, a Klein quartz-plate, or a gypsum-plate with red first order.

4--The centering screws are provided in the nose-piece for accurately centering the various objectives.

5--The upper Nicol (analyzer) is enclosed in one side of a double-chambered box, the other side being left vacant, So that it may be slid in and out of the tube at will, without at any time leaving an opening through which dust may enter.

No. 570, Model Petrographical stand as described, with any of our Huyghenian eye-pieces, in: polished: case with handle; lock and key, drawer for accessories and receptacles for eye-pieces and objectives... $108.00

No. 571, The above with eye-pieces A or B, provided: with cross hairs, eye-piece C (No. 702) provided with micrometer; objectives 3/4 inch (No. 605) and 1/5 inch (Nos. 610 or 611), pliers, slides and covers; magnifying power with tube at standard length, 50 to 485 diameters... $135.00

No. 572, Universal Petrographical Stand, same outfit as No. 570... $133.00

No. 573, The above with same outfit as No. 571... $160.00

No. 574, Professional Petrographical stand, same outfit as No. 570... $210.00

No. 575, The above with eye-pieces A (No. 700) with cross hairs, B (No. 701), C (No. 702) with micrometer, D (No. 703); objectives 2 inch (NO. 602), 3/4 inch (No. 605), 1/5 inch (No. 610 or 611), 1/8 inch (No. 612), pliers, slides and covers; magnifying power 25 to 980 diameters... $200.00