The horizontal measure of hilly ground is invariably taken, both to obtain the plan and area, by the chain and offsetstaff in the following manner. Example. It is required to reduce the hypothenusal line ABC, to the horizontal line A-C. B b A From A, stretch the chain towards B, and suppose it to reach to c. At A stick your offset staff into the ground perpendicularly to the horizon, and let your assistant hold the chain at c close to the ground; at the same time you must elevate the end of the chain to b, or till it is perpendicular to A-b, and you will have the length b-c, the horizontal line to be used in planning or for calculating the area. If b-c is 98 links, then the arrow at c should be put forward two links in each chain until another level is taken. Note 1. When the hill is very steep, it will be necessary to elevate the chain at every thirty or forty links, but once in a chain is generally sufficient. 2. When descending a hill the chain follower should keep his chain hand close to the ground, and the leader should elevate his chain hand as before. 3. Some land-surveyors never use the staff when descending a hill, but drop the arrow this method is not so correct as that by the staff. 4. A fresh level should be obtained at every inequality of the hill, and the arrow should be put forward at every chain, and not at the end of the line, as this method often leads to mistakes. BOOK VI. CASTING; OR THE ART OF MEASURING ON THE PLAN; ALSO TO REDUCE CUSTOMARY MEASURE TO STATUTE, &c. PRACTICAL Surveyors divide their figures on the plan into the triangle and trapezium, the diagonals and perpendiculars of which are measured with the same scale as is used in drawing the plan; and all the crooked or curved fence lines are equalised by the horn ruler, &c., to figures consisting of straight lines and of equal areas, in one fourth of the time than by the common method by the chain and cross in the field, besides being less liable to mistake. A triangle is the principal figure used in land-surveying by the chain only, but a trapezium, when the area is required in the field, or on the plan. PROBLEM I. TO MEASURE THE LENGTH OF A CROOKED FENCE LINE ON THE PLAN WITH A PAIR OF COMPASSES. SUPPOSE ABCD. Take A-B in your compasses, place one foot at B and turn the other in a line with B-C, then extend the point to C. Set one foot at C, and place the other in a line with C-D, and open the compasses to D. Apply the compasses to the scale the crooked fence is plotted by, and you will have the length in chains and links. Note. Roads, rivers, drains, &c., are measured on the plan as above, also a map-meter is used for the same purpose. PROBLEM II. TO REDUCE CHAINS AND LINKS INTO YARDS, &c. Rule.-Set down the dimensions in links, and cut off two figures on the right hand side for decimals. Then multiply by 22, (yards in a chain) and cut off two decimals as before; the figures on the left are yards. Multiply the two decimals by 3, and you will have the answer in yards and feet. Lastly, divide the number of yards by 7, and you will have the answer in roods, yards, &c. Note. Fencing, &c., is generally contracted for by the acre or rood, or by the chain, lineal measure. Seven yards are a rood of fencing, and twenty-eight an acre, lineal measure. Examples. 1. Reduce 1050 links into roods, &c. 10.50 links. 22 2100 2100 7)231.00 33 roods, or 231 yards. 2. In 1520 links, how many roods, &c. ? Answer, 47R. 5Y. 1FT. |