CHAIN

, in Surveying, is a lineal measure, consisting of a certain number of iron links, usually 100: serving to take the dimensions of fields &c.

At every 10th link is usually fastened a small brass plate, with a figure engraven upon it, or else cut into different shapes, to shew how many links it is from one end of the chain.

Chains are of various kinds and lengths; as

1. A chain of 100 feet long, each link one foot, for measuring of large distances only, when regard is not proposed to be had to acres &c, in the superficial content.

2. A chain of one pole or 16 feet and a half in length; especially useful in measuring and laying out gardens and orchards, or the like, by the pole or rod measure.

3. A chain of 4 poles, or 66 feet, or 22 yards, in length, called Gunter's chain, and is peculiarly adapted to the business of Surveying or Land-measuring, because that 10 square chains just make an English acre of land; so that the dimensions being taken in these chains, and thence the contents computed in square chains, they are readily turned into acres by dividing by 10, or barely cutting off the last figure from the square chains. But it is still better in practice to proceed thus, viz, count the dimensions, not in chains, but all in links; then the contents are in square links; and sive sigures being cut off for decimals, the rest are acres; that is four figures to bring the square links to square chains, and one more to bring the square chains to acres.

In this chain, the links are each 7 inches and 92/100, or 7.92 inches in length, which is very nearly 2/3 of a foot. And hence any number of chains or links are easily brought to feet or inches, or the contrary: the best way of doing which is this: multiply the number of links by 66, then cut off two figures for decimals, and the rest are feet: or multiply links by 22 for yards, cutting off two figures.