length of the three sides come even-such as 3, 4, 5 and 12, 16, 20, as shown in Figure 12; and many others, of course. FIGURE 12 THE RULE OF 6, 8 AND 10 This is a rule so extensively used in the building trades and others that it has finally come to be known by the above name. It is derived from the 47th Problem of Euclid, and is used in the manner shown in Figure 13. Measure 6 feet on the end sill of a building and 8 feet on the side sill. If it measures 10 feet across the angle the building is square. This is a very useful rule and easily remembered. It is always available in running lines for batter boards for masonry or lines for walks. By starting from a corner stake into which a nail is driven, measure off on the string or line used and insert a stake to mark the place. Drive a nail into this stake and 12. proceed in like manner on the other side. With a little care and practice, quite a job of surveying can be done by using a few stakes, a ball of string and a tape or 10-foot pole. 'An angle is the opening between two lines meeting at a point. Angles are usually spoken of as being of a number of degrees. The degrees are measured on the circumference, the center of which is on the point of the angle. There are 360 degrees of the circumference of a circle. The surface of the earth is so divided north and south by the parallels of latitude, which are numbered from the equator each way; also east and west by the meridians of longi tude, which are numbered from Greenwich, England. They can be seen on any map. By the use of a protractor, the number of degrees of any angle can be obtained. Figure 14 shows one-half of a circle or 180 degrees. .06 45° 30° 10° €3 FIGURE 14 PLOTTING ANGLES To strike an angle in a field on a large scale where one line is given or can be obtained, measure off from the point of the angle 5710 feet; lay one end of a 10-foot pole at this point. should be swung around so that The other end it also will be 5710 feet from the starting point. Each foot marks off I degree on the circumference of a circle whose radius is 5710 feet. If more than 10 degrees are required, continue as before, keeping the ends of the 10-foot pole always on the circumference of the circle from the starting point. A clear idea of this operation can be obtained from Figure 15. Labor is rest from the sorrows that greet us; |