circles are .785D major and minor axes of an ellipse G d2). this rule Concentric, g. 169, or wn in Fig. ers or the bounded ces of any nts called we say a H FIG. 171. and "b" respectively as shown in ference of the ellipse is found as foll Circumference in which The area of the ellipse in terms which equals 3.1416 × √104 or 2 approximately. The area = .785ab or .785 X 12 X 8 which 75.4 sq. ft. 85. Use of the Square.-The square may be use the diameter of a circle having the same area other circles added together. If the two circles and 3 in. in diam., we lay off on one arm of th 4 in., and on the other 3 in. as shown in Fig. 1 line connecting these points equals the diamet equivalent circle. Proof. The connecting line is 5 in. long, sinc hypotenuse of a right triangle of which 4 in. and the other two sides. Therefore (4)2 + (3)2 = 1416 X 32.0 ft.. h equals ed to find aas two This method can be applied to a ures, such as hexagons, octagons and 86. Rules for Calculating Lengt pulleys are circular in shape the Pulleys of equal diam. Open belt. S FIG. 174. es are 4 in. the square 173. The eter of the is the lengths of belting required to connec the rules for a circle. Case I.-When pulleys are of equ Open Belt. From Fig. 174 it ca length of belt required equals twice pulley centers plus the entire circum If "l" is the length of belt l πα Case II.-When pulleys are of u Open Belt. If the pulleys as sh of unequal size, but the difference great the length of belt is given ap equation, = Crossed Belt.-In this case, Fig. 176, the le is given by the rule 1 = 2√D2 + 82 + πD Case IV. When pulleys are of unequal dia Crossed Belt. For this case, Fig. 177, the 1 eter. spaced centers on a given circumfe or the distance taken on the divi or half the diameter of the circle, th tances AB and OC are equal. To s ever, the chord is not found as table gives the length of chord for for spacing a circle 1 in. in diam B length "7" ameter. length Six equally space centers. Length chord-radius o circle. AB-OC FIG. 178. equal parts from 3 to 82 inclusive. chords given in the table therefo parts of an inch. For circles of diameter larger of multiply the value in the table by given circle. For example, to space a 20-in. equal parts, we find in the table op .2225 which is the correct setting 1-in. circle. For the 20-in. circle w |