Description of a new portable instrument for measuring relative values of gravity to within two or three parts in ten million, specially designed for geophysical exploration. The principles of the design are analysed and the methods for eliminating effects of elastic hysteresis, temperature changes, variations in barometric pressure, etc., are discussed. Also effects of initial stresses in materials, defects in alignment of locking mechanism, inaccurate leveling, etc. These difficulties are serious but seem to have been overcome. Results of preliminary field measurements near Houston, Texas, are presented and some comparison between the type of information given by this instrument and by the torsion balance.