Eidograph in brass with a circular weighted base carrying a graduated square section brass spar in a sleeve engraved “ADIE & SON EDINBURGH” the spar terminating with two pulleys connected by a steel tape through which pass two further graduated spars carrying at their ends a steel point and pencil.
The ends of the main spar, the pulleys and the other two spars are distinguished by the letters “A” and “B”. The scales on all spars are divided into 80 parts to each side of their centres and the verniers on the sleeves within which they slide allow them to be set to 1/10 division. Spars A and B terminate in carriers for the steel point and the pencil and cord operated lever is used to lift the pencil off the drawing paper if required (cord missing). A brass covered lead weight can be set on the main spar. The eidograph was invented by Professor William Wallace of Edinburgh in 1821.
It was used for enlarging and reducing drawings. More accurate than the more common pantograph. It can be set to enlarge or reduce in any proportions. The pantograph can only work according to the divisions engraved on it.
This item was displayed prior to acquisition at the Institution of Municipal Engineers Centennial Exhibition, Brighton, June 1972. (Ref: DINNIS F.R.. A Catologue of the Exhibit Early Uses of Concrete in Edinburgh Roads which includes a selection of Surveying Instruments and an Ediograph in use c. 1872. The Institution of Municipal Engineers, 1972). A copy of this reference is held by the museum.
Th ediograph was also exhibited at the “Exhibition of Civil Engineering Works”, Glasgow, 21 September – 23 October 1977.