The Clarke Formulæ for Computing Latitudes, Longitudes and Reverse Azimuths, for use with either Logarithms or Machine Calculation

Abstract

can be got by slide-rule. The correction for refraction is constant for the set of readings to one star. The eight to ten values for latitude obtained from the observations can be computed very quickly, and one immediately gets some idea of the accuracy of the observation, and can, if necessary, cut out any doubtful values. To obtain longitude, one can assume that the chronometer has kept the same rate during the same series of observations, so that the computed results can be meaned, and this will give the value for chronometer error on L.S.T. or L.M.T. at the mean of the times of the various observations. Next find out the chronometer error on Greenwich time for this mean value, correcting it, of course, for rate. The sum or difference of these two values will give the longitude. This is a quicker method than correcting each computed value for chronometer error and obtaining the value for longitude for each observation, which then has to be meaned. It is hoped that these notes may be of assistance to those who have to fix Astro-Radio points, and I hope that others too will contribute their experiences, because saving of time is of vital importance to any survey work in the back blocks of the world.