Rod (unit)

The rod or perch or pole is a surveyors tool^[1] and unit of length equal to 5¹⁄₂ yards, 16¹⁄₂ feet, ¹⁄₃₂₀ of a statute mile or one-fourth of a surveyor's chain and 5.0292 meters. The rod is useful as a unit of length because whole number multiples of it can equal one acre of square measure. The 'perfect acre'^[2] is a rectangular area of 43,560 square feet, bounded by sides 660 feet by 66 feet long (660 ft long × 66 ft wide), or 220 yards by 22 yards long (220 yd/ long × 22 yd wide), or 40 rods by 4 rods long. Thus, an acre is 160 square rods. Since the adoption of the international yard on 1 July 1959, the rod has been equal to exactly 5.0292 meters.

A rod is the same length as a perch, also sometimes called a pole which measure using cordage^[3] or wood, slightly antedated the use of both rods and surveyors chains, made of more dimensionally regular materials. The measure also has a relationship to the military pike of about the same size and both measures^[1] date from the sixteenth century,^[3] when that weapon was still utilized in national armies. The tool, normally configured as a metal rod with eye-ends (loops that could be hooked together), was used commonly until quite recently, when it was supplanted by electronic tools such as surveyor lasers (Lidar) and optical target devices for surveying lands. Surveyors rods and chains are still utilized in rough terrains with heavy overgrowth where laser or other optical measurements are difficult or impossible. In old English, the term lug is also used.^[4][5]

History

Until English King Henry VIII seized the lands of the Roman Catholic Church in 1536,^[1] land measures as we now know them were essentially unknown.^[1] Instead a narrative system of landmarks and lists was used. Henry wanted to raise even more funds for his wars than he'd seized directly from church property (he'd also assumed the debts of Monasteries^[1]), and as James Burke writes and quotes in the book Connections: the English Monk Richard Benese "produced a book on how to survey land using the simple tools of the time, a rod with cord carrying knots at certain intervals, waxed and resined against wet weather. Benese who poetically described the measure of an Acre in terms of a perch:^[3]

The practice of using surveyor's chains, and perch length rods made into a detachable stiff chain came about a century later when iron was a more plentiful and common material. A chain is a larger unit of length measuring 66 feet (20.1168 meters), or 22 yards, or 100 links,^[6] or 4 rods (20.1168 meters). There are 10 chains or 40 rods in a furlong (eighth-mile), and so 80 chains or 320 rods in one statute mile (1760 yards, 1609.344 m, 1.609344 km); the definition of which was set by Royal surveyor (called the 'sworn viewer'^[7]) John Ogilby only after the Great Fire of London (1666).

An acre is defined as the area of 10 square chains (that is, an area of one chain by one furlong), and derives from the shapes of new-tech plows^[2] and the desire to quickly survey seized church lands into a quantity of squares for quick sales^[3] by Henry VIII's agents; buyers simply wanted to know what they were buying whereas Henry was raising cash for wars against Scotland and France.^[3] Consequently, the surveyor's chain and surveyor rods or poles (the perch) have been used for several centuries in Britain and in many other countries influenced by British practices such as North America and Australia. By the time of the industrial revolution and the quickening of land sales, canal and railway surveys, et al. Surveyor Rods such as used by George Washington were generally made of dimensionally stable metal—semi-flexible pinky-finger-tip-thin drawn wrought iron linkable bar stock (not steel), such that the four folded elements of a chain were easily transportable through brush and branches when carried by a single man of a surveyor's crew. With a direct ratio to the length of a surveyor's chain and the sides of both an acre and a square (mile), they were common tools used by surveyors, if only to lay out a known plottable baseline in rough terrain thereafter serving as the reference line for instrumental (theodolite) triangulations.

In ancient cultures

The Ancient Roman units of measurement of length included a rod or pertica (also decempeda) of 10 pedes, which was equivalent to about 2.96 m; the related unit of square measure was the scrupulum or decempeda quadrata, equivalent to about 8.76 m².^[8]

In continental Europe

A standard at the City Hall in Münster, Germany from 1816; the bar shown is one "Prussian Half Rod" (1.883 m) long.

Units comparable to the perch, pole or rod were used in many European countries, with names that include French: perche and canne, German: Ruthe, Italian: canna and pertica, Polish: pręt and Spanish: canna. They were subdivided in many different ways, and were of many different lengths.

Based on data from the following:

• ^N - Niemann (Quedlinburg and Leipzig - 1830).^[9]

In Britain

In England, the rod is first defined in law by the Composition of Yards and Perches, one of the statutes of uncertain date from the late 13th to early 14th centuries.

The length of the chain was standardized in 1620 by Edmund Gunter at exactly four rods.^[10][11] Fields were measured in acres, which were one chain (four rods) by one furlong (in the United Kingdom, ten chains).^[12]

Bars of metal one rod long were used as standards of length when surveying land. The rod was still in use as a common unit of measurement in the mid-19th century, when Henry David Thoreau used it frequently when describing distances in his work, Walden.^[13]

Modern use

The rod was phased out as a legal unit of measurement in the United Kingdom as part of a ten-year metrication process that began on 24 May 1965.^[14]

In the USA, the rod, along with the chain, furlong, and statute mile (as well as the survey inch and survey foot) are based on the pre-1959 values for United States customary units of linear measurement. The Mendenhall Order of 1893 defined the yard as exactly ³⁶⁰⁰⁄₃₉₃₇ meters, with all other units of linear measurement, including the rod, based on the yard. In the post-1959 system, the fundamental unit of length is the inch, defined as exactly 2.54 centimeters. However, the above-noted units, used in surveying, retain their pre-1959 values.^[15]

Despite no longer being in widespread use, the rod is still employed in certain specialized fields. In recreational canoeing, maps measure portages (overland paths where canoes must be carried) in rods; typical canoes are approximately one rod long.^[16] The term is also in widespread use in the acquisition of pipeline easements, as the offers for an easement are often expressed on a "price per rod".^[17]

In the United Kingdom, the sizes of allotment gardens continue to be measured in square poles in some areas, sometimes being referred to simply as poles rather than square poles.^[18]

In Vermont, the default right-of-way width of state and town highways and trails is three rods (15.0876 m).^[19] Rods can also be found on the older legal descriptions of tracts of land in the United States, following the "metes and bounds" method of land survey;^[20] as shown in this actual legal description of rural real estate:

LEGAL DESCRIPTION: Commencing 45 rods East and 44 rods North of Southwest corner of Southwest 1/4 of Southwest 1/4; thence North 36 rods; thence East 35 rods; thence South 36 rods; thence West 35 rods to the place of beginning, Manistique Township, Schoolcraft County, Michigan.^[21]

Area and volume

The terms pole, perch and rod have been used as units of area, and perch is also used as a unit of volume. See square perch and rood. As a unit of volume, Rod equals to 1000 cubic feet.^[22]

See also

• Perch
• Chain (unit)
• Furlong
• Imperial units
• English units
• United States customary units
• anthropic units

References