Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

OF ENGINEEBING FOKMULÆ. Measuhement of Heights with Sextant. (J. T. Hurst.) Multiplier. Angle. Divisor. Angle. O 1 O 1 1 45 0 1 45 0 2 63 26 2 26 34 3 71 34 3 18 26 4 75 58 4 14 2 5 78 41 5 11 19 6 80 32 6 9 28 8 82 52 8 7 8 10 84 17 10 5 43 Set the sextant to any angle in the Table, and the height will equal the distance multiplied or divided, as the case may be, by the number opposite to it. Reduction of Base Lines to Level of Sea. L = Length of base line measured in feet. h = Height of base line above sea level in feet. c = Correction in feet to be subtracted from the length, of the base line. LA ° “ 20,890,000 Plotting Angles without a Protbäctob. On a given line prick off 100 with any conve- nient scale, and from the point so pricked off lay off at right angles with the same scale the natural tangent due to the angle (see Table of Natural Sines, &c.); or strike out a portion of a circle with radius 100 and lay off a chord — 2 sin. of half the angle required.