## A Collection of Tables and Formulæ Useful in Surveying, Geodesy, and Practical Astronomy; Including Elements for the Projection of MapsThis historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1853 edition. Excerpt: ...in the magnetic moment of the deflecting magnet, produced by the earth's inducing action, are determined from experiments with the Bifilar magnetometer--when this instrument is not used, as is the case in our observations and upon magnetic surveys generally, the formula becomes: THT'('-s4o-f$fx(1 +?) x(i-(('-0?) where: T and T' = the true and observed times of vibration, r = the rate of the chronometer T, ."' I--when gaining a and a' = the initial and terminal semi-arcs of vibration in parts of radius, =-= the ratio of the torsion and magnetic forces, t = the temperature of the deflecting magnet during the experiments of deflection, /' = the temperature of the deflecting magnet during the experiments of vibration, q = the change of magnetic moment of the deflecting magnet for 1 of temperature. IX ft' The value of-rg-is found by the formula: = a'dd'X 0.00007272s lb where d, d' denote the semi-arcs of vibration in divisions of scale, and a, the angular value of 1 division. q = a. n. cot u. t----10 where o = the arc value of 1 division of scale in terms of radius, h = the difference of scale readings corrected for changes of declination, t--to = the corresponding difference of temperature, u = the angle of deflection at the lowest mean temperature. Final calculation of the results., ervations of deflection, we have By those of vibration, ... m X = B By the observations of deflection, we have--= A The correction for arc, in an extreme case when the initial semiarc was 36 sca1e divisions (1 40' 30"), amounted to only 0.000037. The correction for rale, when the chronometer loses 3 seconds per day, is 0.000084. From examples in Riddell's Instructions, the value of the horizontal intensity is not carried beyond four decimal figures, and as... |

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