715.—The Instruments Generally Employed for Measuring Land are chains, steel bands, and tapes. Where roads are roughly measured, pedometers are commonly used. Where very exact measurements are required, rods have been used. Rough approximate measurements are obtained by stepping, with the use of the passometer to count the steps.
716.—Land Chains.—Although these are made in many qualities the forms vary very little. They are too well known to need much description. In the British Isles and some of our colonies the chain of 100 links, equal to 66 feet, the invention of Edmund Gunter about 1620, is generally used, 10 square chains (100,000 square links) giving the statute acre, presenting a decimal system of measurement much in advance of any other at the present time. The best land chains are made of steel, which is afterwards hardened and tempered to spring temper, in the process of which the surface is burnt off with asphalt varnish in order to produce a covering to resist the rusting effects of moisture. Steel chains are made light and strong. The light chain, of No. 12 Birmingham wire gauge, weighs under 5 lbs. The strong chain, of No. 8 B.W.G., weighs about 12 lbs. A light chain of 50 links, of weight under 3 lbs., is sometimes used with the complete chain of 100 links for taking offsets.
Fig. 330.—Land chain and arrows.
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All the best chains, whether of steel or iron, are made with long links formed by turning up the ends of a length of wire. Three small oval links are placed between each pair of long links. These three interval links are found to cause the chain to kink less than when only two are used. Each oval link is sawn through at the meeting line, which is brought up on one flat side of the oval in bending it from the wire. The saw-cut forms the point of adjustment. The small link is afterwards re-sawn and closed to shorten it, or forced open to lengthen it. There are generally four swivels in the length of the chain, two of which are at the handles: these prevent the chain from becoming twisted in turning the handles over in use. A swivel is shown Fig. 331 at S. Iron chains are sometimes galvanized to prevent rust. This process, however, makes the chain much more brittle, and cannot be recommended. It may be noted that all link chains lengthen with use.
717.—Tellers are small pieces of brass suspended to the chain by a spare link placed at every ten links. They divide the chain decimally from either end equally. Proceeding from one end of the chain the tellers read 10, 20, 30, 40, 50, and the other end they read by subtraction from the complete chain: 100 - 10 = 90, 100 - 20 = 80, 100 - 30 = 70, and 100 - 40 = 60. Fig. 331 shows detached pieces of chain with value of the tellers figured under. S inserted swivel. The 50 teller shows the link attachment. A shows the position at which the arrow or other mark is placed to commence or finish the chain measurement, the handle being included in the first link. These tellers are liable to catch and get dragged off in chaining. When this chain is used abroad, or far from home, it is well to have an extra set of tellers to repair losses.
Fig. 331.—Gunter's land chains.
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