Treatise on the principal mathematical instruments employed in surveying, levelling, and astronomy : explaining their construction, adjustments, and use. With an appendix, and tables / by Frederick W. Simms.

  • Simms, Frederick Walter, 1803-1865.
Date:
1834
Catalogue details

Licence: Public Domain Mark

Credit: Treatise on the principal mathematical instruments employed in surveying, levelling, and astronomy : explaining their construction, adjustments, and use. With an appendix, and tables / by Frederick W. Simms. Source: Wellcome Collection.

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    A DESCRIPTION OF THE PRINCIPAL INSTRUMENTS EMPLOYED IN SURVEYING, LEVELLING, # ASTRONOMY, WITH THEIR ADJUSTMENTS AND USE. SURVEYING INSTRUMENTS. THE LAND CHAIN. Gunter’s Chain is the one now commonly used in taking the dimensions of land; it is sixty-six feet, or four poles, in length, and is divided into 100 links, each of which is joined to the next by three rings ; the length of each link, including the connecting rings, is 7,92 inches, and at the end of every tenth link is attached a piece of brass (each of a different shape,) for more readily count¬ ing the odd links. “ The English acre contains 4840 square yards, and Gunter’s chain is 22 yards in length, and the square chain, or 22 multiplied by 22, gives 484, exactly the tenth part of an acre; and ten square chains are equal to one acre; consequently, as the chain is divided into 100 links, every superficial chain contains 100 multiplied by 100, that is 10,000 square links ; and 10 superficial chains, or one acre, contains 100,000 square links. If therefore the content of a field, cast up in square links, be divided by 100,000, or, (which is the same thing) if from the con¬ tent we cut off the last five figures, the remaining figures towards the left hand give the content in acres, and consequently the num¬ ber of acres at first sight; the remaining decimal fraction, multi¬ plied by 4, gives the roods, and the decimal part of this last product, multiplied by 40, gives the poles or perches.” Short distances, or off-sets from the chain line, are usually mea¬ sured with a rod, called an off-set staff, the most convenient length for which is 6 feet 7,2 inches, being equal to 10 links of the chain, and it should be divided accordingly. With the chain must be provided ten arrows, which may be made of strong iron wire, about 12 or 15 inches long, pointed at one end for piercing the ground, and turned up at the other, in the form of a ring, to serve as a handle: their use is to fix in the ground at each extremity of the chain whilst measuring, and to point out the number of chains measured. B