Mexican gravity‐stations in 1930 and first calculations and corrections for topography and isostasy

In continuation of the program of gravimetric work ordered by the Department of Geographic and Climatological Research during the year 1930, twelve gravity-stations were observed, all in the central plain of our Republic, besides the two determinations at the base-station in Tacubaya. The apparatus used was constructed by the firm of Berger and Sons of Boston, and consists of three invariable bronze pendulums, one-quarter meter in length and one-half second in oscillation, besides the thermometer- pendulum, coincidence- or flash-apparatus, interferometers, chronometers, etc., similar to those used by the United States Coast and Geodetic Survey, with which differences of gravity between two given places are obtained with great precision. Knowing the value of the intensity of gravity in Tacubaya, which was determined in 1912, with relation to that at Washington, all our observations have been reduced to obtain the differences In gravity between the stations in the field and the known value for the base-station at Tacubaya. The observations in this last city, made before and after each circuit, were for the purpose of testing the invariability of the mass of the pendulums and, consequently, the periods of oscillation and to correct the field-values for the resulting small difference. These are found in the “Table of the duration of one oscillation in Tacubaya” and in the curves of the periods of oscillation deduced from the same, which follow at the end of this article.