16 ENGINEERING ON THE FARM 



ground when the end is held high on sloping ground (Fig. 2). 

 The uniform pull to be exerted by the chainmen on a chain 

 or tape 100 feet long is approximately 12 pounds. 



Area measurements. In measurements of area the same 

 units are used as in lineal measurements, except that the 

 measurement extends in two directions. The common term 

 for expressing area measurements and their equivalents 

 in feet are: by the square foot, equivalent to 144 square 

 inches, used to express floor, window, wall, and other areas 

 and limited to no definite line of work; and the square yard, 

 equivalent to 9 square feet, a larger unit of area usually 

 applied to plastered walls, paved areas, carpets, etc. The 

 acre is the standard unit for land measurements and is 

 equivalent to 10 square chains or 160 square rods or 43,560 

 square feet. When it is desired to express the extent of large 

 areas of land, the term section or square mile is used, each 

 of which is theoretically the equivalent of 640 acres. In 

 very large areas of land the term township is used. Theo- 

 retically, this is a tract of land 6 miles square, containing 

 23,040 acres. Actually, the government section or township 

 seldom contains the exact theoretical amount, owing to the 

 conditions explained in the chapter on land surveys. 



Surfaces. The circle contains a greater area than any 

 other plane figure bounded by an equal perimeter or outline. 

 The areas of circles are to one another as the squares of their 

 diameters. Any circle the diameter of which is double that 

 of another contains four times the area of the other. The 

 area of a circle is equal to the area of a triangle the base of 

 which equals the circumference and the perpendicular of 

 which equals the radius. 



Diameter X 3 . 1 4 1 59 = circumference 



Diameter X . 8862 = side of an equal square 



Diameter X - 707 1 = side of an inscribed square 



Diameter squared X .7854 = area of a circle 

 Radius X6. 28318 = circumference 



Circumference -5- 3 . 14159= diameter 



