An instrument that will simulate the anomalous gravity effects of a subsurface body, having a density differing from that of its surroundings, is described. The device makes use of the similarity between the gravity equation and Lambert's cosine &thgr; law, and enables the geophysicist to synthesize the anomaly producing body in a time much shorter than that required for conventional computational methods. The accuracy that can be expected is ±5% of the maximum anomaly within limitations noted in the paper.