CARPENTER’S RULE,
LONGPORT HOUSE, NEWINGTON
This object was found in a roof space at Longport House at Newington, near Folkestone. The house had to be dismantled in 1992 as it lay within the construction zone of the proposed Channel Tunnel terminus. The dismantling of Longport House was undertaken by both Canterbury Archaeological Trust and the Weald and Downland Open Air Museum. The rule is a rare example of a well preserved early post-medieval wooden measuring tool.
Date: Post-medieval (AD 1635)
Origin
The rule was found amongst loose debris that had collected above a plaster ceiling at Longport House, hidden beneath a water tank. It was found in two pieces, but in very well preserved condition. Numerous small bore-holes had been caused by insect larvae. Analysis of the wood indicates the artefact was made from the wood of a maple tree. Maple wood provides a strong, even-grained material and has been used for turning and carving objects such as domestic utensils (for example, spoons and bowls), and for components in the textile industry (for example, weaver shuttles). Where the rule was made remains unknown.
Longport House was a medieval timber-framed house that once stood end-on to the A20 carriageway near Folkestone, within the parish boundary of Newington. The house was once a larger hall-house, accompanied by a range of outbuildings suggesting it was formerly a farm.
Use
The object is a wooden two-foot (24 inch) rule. Rules such as this would have been the standard measuring tool of early modern craftsmen. This example in incised with decorative patterns on one side and tables to assist with a carpenter’s calculations on the other. It bears the date 1635.
The rule is equipped with scales to assist in the measurement of board and timber, and in this form was known as the carpenter’s rule. These scales allowed arithmetically unskilled users to ‘calculate’ instrumentally, simply by following manual procedures.
Discovery
The rule was found whilst clearing the roof space at Longport House at Newington, near Folkestone. The house was dismantled in 1992 ahead of the construction of the Channel Tunnel terminal. The building was subsequently reconstructed at the Weald and Downland Open Air Museum in West Sussex in 1995 where it was used for many years as the museum’s entrance, shop and office. The downstairs area is now used as a temporary exhibition space.
The oldest surviving example (in this country) of a rule comes from the wreck of the Mary Rose (1545) in the form of a straight piece of oak. Early craft objects have a low survival rate in museum collections and the Longport rule is only the second straight format instrument to be reported.
Whilst it is called a Carpenter’s Rule it may have belonged to one of a range of other craft practitioners as, despite its name, the instrument was not exclusively reserved for workers in wood.
Current Location
Canterbury Archaeological Trust archives.
Catalogue Entry
Site code: LH92
It is a rectangular piece of maple wood, with rounded corners and a cross-section of variable thickness. The rule is thicker at one edge than the other: 5.9mm compared to 8.5mm in a representative section, with a maximum thickness of 9.0mm at that section. It is cracked and worm-eaten, and there is a break about six inches from one end. There are missing fragments from one edge of the smaller piece.
The rule carries several scales and tables, the numerals of all of which have been punched with a single set of tools. There are some minor errors such as numerals upside down and punched figures corrected.
The first face carries two inch scales, one against each edge, divided to halves, quarters and eighths, and numbered every inch [0]-24, 24-[0]. Both scales have alternate half inches hatched, using a variety of hatching styles. There is no clear pattern to the distribution of the hatching styles along the rule.
The central band between the inch scales is filled with engraved geometric decoration. There are four motifs, each of which is repeated in its own six-inch section:
- diamond strapwork with dotted straps and central circles (punched zeroes) (1” module; last inch partially engraved);
- intersecting arcs with dotted strapwork (1” module), the arcs centred on the half-inches of the inch scales;
- concentric intertwined circles (½” module);
- diamond strapwork with plain straps and central dots (1” module).
The reverse face carries what is presumably the date of the rule, “1635”, punched at the midpoint against one edge. Against the other edge is a non-linear scale – a line of timber measure, running from 9 to 36 and subdivided to half inches. A matching timber scale also appears on the contiguous edge, divided only to inches. Beyond 20, when the divisions become ever more closely spaced, the numbering of the scales is abbreviated: on the edge scale the leading tens value is dropped, so 21 appears as simply 1, 22 as 2 and so on (although 30 appears as 3 rather than 0); the numbering of the inches on the face scale continues in full to 26 and in part to 30 (as 7, 8, 9 and 3), but no further.
Towards the end of these scales there are various misplaced divisions and misalignments: the interval between 22 and 23 is too large because it is divided into 3 rather than 2 parts on the face; the 26 division is out of register between the face and edge scales; and there are also misplaced divisions around 32 and 34 on the edge.
The reverse face also carries two numerical tables: a table of timber measure which duplicates and extends the timber scales, and a complementary ‘table of roots’.
The rule was examined and described by Dr Stephen Johnston, Museum of History of Science, (University of Oxford) as “an early and highly unusual example of a carpenter’s rule. It bears witness to the complex relationship between traditional craft practices and the rapidly expanding tradition of practical mathematics in seventeenth-century England”.
The Mary Rose Carpenter’s Rule can be viewed here: https://maryrose.org/meet-the-carpenter/
