I bought this chain on an on-line auction site in 2012 after it was brought to my attention by befriended collector John Bradley. Although I already had an imperial chain, I still found it worthwhile adding it to my collection as this is not just another chain. This chain is a standard chain, 66 feet in length.

The word 'chain' not only is the name of this instrument, but also a unit of length, which measures 66 feet, or 22 yards, or 100 links, or 4 rods (20.1168 m). There are 10 chains in a furlong, and 80 chains in one statute mile.

This chain was made by Doyle & Son, London, England and is in very good shape. Being a standard chain means it is an official calibrated length measure. It came complete with its original box (see figure 1) and grapes (a kind of staples used to fixate the end of the chain, see figure 5). The chain has dated hallmarks and has been certified several times between 1891 and 1963. In addition to that it bears an Indenture Number that was issued on 19 January 1835.²

The chain is made of steel with brass handles and brass reference blocks (see figure 2), 66 feet (20.1168 metres) in length and made of twenty-two 34" and two 24" links. The shorter ones are the end links with the brass handles and reference blocks. The links are directly joined together without using additional rings as with the other chains in my collection (see figure 11). Each long link has two different eyes at its ends; one symmetrical and one asymmetrical in shape to avoid stress when folding the chain together (see figure 12). There are no tallies or other markers along the chain to indicate intermediate measures.

The handles did not play a direct role in the measurements as with the other chains in my collection, but were simply for holding, stretching and fastening the chain using the grapes. One of them is finely engraved with the indication of the length '66ft Standard' (see figure 15).

The reference blocks at the shorter links have a line engraved in them that serve as the reference for the total length of one chain (see figure 14). Both are stamped with a Victorian hallmark from 1891, while one of them has been stamped with several additional hallmarks from 1913, 1923, 1936, 1943, 1953 and 1963 and crowned hallmarks for Edward VII, George V and George VI (see figure 3).

On the other side one of the reference blocks the Indenture Number '615' is stamped into it (see figure 13). This indenture number refers to the original opening in a ledger in which the whole history of this chain was recorded. The number was issued on 19 January 1835 to Northumberland County and most probably is the manufacturing year of this chain.²

Although the chain is one of the longest-in-use instruments in surveying, this type of chain is of a more recent design. Where the oldest reference to a 'wyer lyne' dates back to 1590,⁵ this particular chain was designed around 1809.

The first mention and depiction of a survey chain of this design can be found in the article 'An Account on a Trigonometrical Survey of Mayo' by William Bald, "...Civil Engineer, Member of the Geological Society, London, and M.R.I.A".⁶ While preparing the survey of the county of Mayo he ordered "...Mr. Edward Troughton, of London, to make a chain ... which might be applied to a flat surface of soil ... and he sent ... one ... of a simple but accurate construction." (see adjacent sketch).⁶

Chains were usually supplied with a set of 11 or 6 ground pins or arrows that would have been used with the chain to count the sections measured with it. The Mayo chain also was supplied with "Arrows to be applied when used on ordinary occasions".⁷

Clearly the chain was made for other occasions than the ordinary ones as the sketch tells us it was to be "...used in measuring the bases for the Trigonometrical Survey of Mayo".⁷ In total seven baselines were measured, six of which were used to scale the trigonometrical survey (the seventh was destroyed by "...some idle person...").⁶ The use of this chain was thus altogether different than that of the other chains in my collection as those were merely for surveying at a local level (i.e. cadastral works etc.).

For the baseline measurements the chain was supplied with "Grapes for holding the Chain to be applied within the Handle[s]" (see figure 5).⁷ A plate with a moveable index could be fastened to the ground and used "...when measuring by lines of Coincidence" to connect two chain measurements to each other.⁷

Being mainly used for baseline measurements the number of chains of this type must have been limited and mainly used by governmental departments. The fact that it was delivered with a box is an indication for the status this kind of chain had.

This particular chain has been used by the District Inspector of the 505 District of the County of Northumberland, Alexander Young. According to the label in the lid of the box, the District Inspector was stationed at the Moothall in Newcastle on Tyne (see figure 6). Later, the chain was handed over by what we may assume was his successor, James Tough. So far I have been unable to trace both Alexander Young or James Tough, or even the department they worked for.

The Mayo chain was calibrated "... at the temperature of 65°, of Fahrenheit's thermometer..." (18.3°C),⁶ and presumably this chain was calibrated at the same temperature. The Mayo chain was used to measure a two mile stretch over ice. The measurement was repeated and found to be within one inch of the first result, which is a repeatability of 1:127,000 or 8mm/km!⁶

Although seemingly simple instruments, chains could produce very accurate results and were preferred above angle measurement devices up to the 18^th century.⁸ In 1810 Nesbit wrote his first edition of a textbook on surveying, which would be continuously updated and reprinted well into the 20^th century. The first edition did not contain any reference to the theodolite, which he explained in the 1820 second edition by stating that

Chains were gradually replaced by steel tapes, like the ones by Tibaut Desimpelaere and Ahrend in my collection.