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Williamson-Ross Projector


A large, well-worn wooden case contains a metal optical instrument in three main parts. The box is painted black with white lettering stenciled on the front surface, and has a rectangular cross section. Two latches on the front surface secure the hinged lid.

2019.for.22.1: The largest metal component within is finished primarily in black wrinkle paint. It features several adjusting screws in various orientations. At one end is a circular optical element. A glass slide featuring an aerial photograph is secured to one face of this element.

2019.for.22.2: A cylindrical element that tapers at one end and a projection lens at the other. The tapering end has an attachment, presumably for air cooling.

2019.for.22.3: A bulb and socket with an electrical cord attached to the rear. This screws into the tapering end of 2019.for.22.2.

Accession Number: 2019.for.22

Alternative Name: Multiplex Projector, Mapping Projector

Primary Materials: Iron alloy, Wood, Glass.


Two labels on the interior of the box read as follows:
“This Projector MUST be fed with cooling air BEFORE switching on Where anti whistle vales are fitted in the 3/4 hoses they Should preferably be removed.”
“Williamson-Ross Mapping Equipment// Bridging trials with grids have been made with these Projectors working in numerical order from left to right.// This Prijector No. 3180 was on the// Right of No. 3179// Left of No.”

A maker’s label on 2019.for.22.1 provides the following information:
“Serial No. 2256”, “Type M.P.C.”
The lens in this element carries the following information:

The lens attached to 2019.for.22.2 carries the following information:
“Steinheil München Orthostigmat 1:4.5 f=35mm VL Nr. 698111”

Dimensions (cm):

Case: Height = 34.5, Width = 62.5, Length = 18.5.


This is a cartographic instrument. It was used as part of a larger apparatus that generated a stereoscopic model of terrain using aerial photographs. This stereoscopic model was used to produce maps with topographic information.


Very Good: This appears to be in functional condition. 2019.for.22.1: Some rust on certain bearing surfaces and fasteners, as well as some material (possibly old adhesive) on some surfaces; 2019.for.22.2: this is lightly worn around the edges.

Associated Instruments:


Williamson Manufacturing Co., London, England.

Date of Manufacture: After 1945.


This artifact used to create maps from aerial photographs at the University of Toronto Department of Forestry.

It was acquired on July 3rd, 2019 from Tony Ung at the Department of Forestry.

Additional Information and References:

Abrams, Talbert (1944). <i>Essentials of Aerial Surveying and Photo Interpretation.</i> New York and London: McGraw-Hill Book Company, Inc.

Tropey, Lyle G. (1950). <i>Handbook of Aerial Mapping and Photogrammetry.</i> Cambridge: Cambridge University Press.

Moffitt, Francis H. (1959). <i>Photogrammetry.</i> Scranton, Penn: International Textbook Company.

Historical Notes:

This projector is part of a much larger apparatus. At least two such projectors were required to create a stereoscopic image, but the apparatus included a table, frame, cooling system, photographic printer, and other instruments.

In order to use this instrument for cartography, aerial photographs were printed on small glass plates called diapositives using an instrument called a reduction printer.

These small photographic plates were mounted in projectors such as this one. Each projector has six adjustable motions (x/y and z axes, and three rotational axes). The projectors were lit by powerful 24v lamps that required air cooling. The projectors were aligned on a horizontal bar representing the line of flight of the aircraft. [Moffitt 262] The projectors cast an image on a very level drawing surface.

These projectors were used in sets of multiple instruments. One stereoscopic image required two projectors, one with a red filter, and one with a blue or green filter. When viewed with coloured glasses this produced a stereoscopic model or the terrain, the projectors becoming “miniature replicas of the aircraft camera”. [Tropey 131]

Topography was derived from this model using a “plotting table”, or “tracing-table platen” instrument with a vertically adjustable floating mark consisting of a lighted point. The mark is used to follow the contours of the terrain of the stereoscopic models at a given height. A pencil records the movement of the plotting table. The process of tracing the contours of the stereoscopic image required operator skill.

Cameras could be used in several overlapping pairs creating a “multiplex extension” or “bridge.

Similar instruments were also produced by Zeiss and Baush and Lomb.