There is one instrument of use in the study of terrestrial gravity which has not yet been employed in the western hemisphere, though it has to a limited extent in Europe. This instrument is the Eötvös balance. It should be tried, I believe, in making the proposed minute investigation of gravity in a level region of limited extent. To judge by accounts of work done with the balance in Europe it would certainly supplement the pendulum advantageously in the proposed gravity survey and might largely supersede it. This does not by any means signify, however, that the balance is always and everywhere a substitute for the pendulum. This is not the occasion for an exposition of the principles of the instrument, but it may be said that the Eötvös balance connects the results at adjacent points in a limited region with one another in a way that the pendulum cannot well