To express gradients per cent. (page 332), in angular measure, multiply the rate per cent. by 34.3; the product will be given in minutes of a degree. If the gradient per cent. be multiplied by 57.14, the result will be expressed in hundredths of a degree. SOUND. At freezing temperature, 32 degrees Fahrenheit, in calm air, the velocity of sound may be assumed 1100 feet per second. For lower temperatures subtract, and for higher add, a half foot per degree. The intensity of sound varies inversely as the square of the distance. The velocity varies directly as the temperature. It is nearly four times as great in water as in air; and in wood ten to sixteen times as great. AMERICAN AND FRENCH EQUIVALENTS. LINEAR MEASURE. 1 inch = 2.54 centimetres; 1 centimetre = .394 inches. = .3048 metres: 1 metre 3.2809 feet. 1 foot 1 yard = = 3 feet.9144 metres; 1 metre = 1.0936 yards. 1 square inch = 6.4515 square centimetres. 1 square centimetre = 0.1550 square inches. 1 square foot = 0.929 square metres. 1 square metre = 1.19659 square yards. 1 square acre = 43560 square feet 4840 square yards. 1 square hectare = 2.4711 acres = 11960 square yards. 1 square kilometre .3861 square miles. 1 square mile = 2.5899 square kilometres. 1 square rod = 272.25 square feet = .00259 hectares. AMERICAN AND FRENCH EQUIVALENTS. CUBIC MEASURE. 1 cubic inch = 16.383 cubic centimetres. 1 cubic centimetre = .0610 cubic inches. PAGE Curves, compound, - to find radius, length, degree, apex distance, chord, mid- with transit and chain hints as to field-work protractor for slackening grade on . Curves, simple, location of,- how to proceed when the P. C. is inaccessible to shift the P. C. in order to strike a fixed tangent to change radius from same P. C. in order to strike a fixed tan- how to proceed when the P. C. C. is inaccessible 161 51 . 52, 56 96 97 94 127, 128 95 to compound a curve in order to strike a fixed tangent 98 to shift a P. C. C. in order to strike a fixed tangent to compound into a tangent intersecting main curve on concave 102 to compound into a tangent intersecting main curve on convex angles unequal, tangent points fixed, radii equal to shift a P. R. C. in order to strike a fixed tangent to connect curves of contrary flexure by short tangents from a convex curve . 52, 55 145, 146 89 103 104 to substitute a curve for a tangent connecting two curves 109 Curves, miscellaneous-continued. trackmen's table of curves and spring of rails vertical curves, to calculate to project Datum in levelling Decimals of an acre per 100 feet for various widths, Table IV. PAGE 143 36 39 27 151 50 57, 64, 68 68 82 52, 55 81 50 155 130, 132 141 142 30 54 269 148 153 79, 85 27 70 33, 34, 35 129 130 135 136 132 133 134 134 12 14 15 49 87 332 86 81 |