Description and Notes:
Based on the proportional properties of the edges of the similar triangles divided within a four-bar parallelogram linkage, the pantagraph (pantograph) is a precision instrument devised in the seventeenth century which can be used for copying, reducing, and enlarging drawings. However in practice it is principally used for making reductions. The one presented here is made in England by Stanley London, and it is described in the 32nd "U" edition of the Stanley Catalogue (p. 149) as the "improved pantagraph." According to A Descriptive Treatise On Mathematical Drawing Instruments by W. F. Stanley, the improvements are mainly made in three aspects. Firstly, to increase the rigidity of the instrument and at the same time to reduce its total weight, all of the links are constructed by using square sectioned brass tubular bars. This remedy however was adopted by Stanley from the concept first introduced by one M. Gavard of Paris. Secondary, to avoid interferences between the links when the instrument is operated at nearing closed position; the fulcrum and the tracer are arranged on the same side of the bars instead of on the opposite sides as the old ones. Thirdly, the shape of the weight is changed from circular to triangular to increase the working space of the device.
This pantagraph equipped a simple mechanism to raise the pencil holder* off the drawing surface. It is activated by a cable connecting a trigger near the tracer and a level at the pencil holder through a set of pulleys attached on the links. This feature is particularly convenient when copying disconnected lines or passing the areas which are not intended to be reproduced. The length of the longest link of this pantagraph is 32 inches, and it is capable of making reductions from 1/1 to 1/12. A set of five casters are installed underneath the bars to eliminate frictions and to increase its mobility. The storage case is made of mahogany.
* The original brass pencil holder is missing, the one shown in the photos is a later replacement with a wooden top.