SOME years ago investigations were carried out concerning attractive forces between glass and quartz bodies with flat polished surfaces1. Due to the well-known hygroscopic behaviour2 of these surfaces, however, silica-gel obstacles were always present on the plates. These obstacles had a tendency to decrease the attractions and even to turn them into repulsions. Therefore metal plates have now been used instead of glass or quartz. The technique used was similar to that described earlier1. The main difficulties were caused by dust particles, and general agreement was found with the conclusions obtained in recent work3 on the influence of dust particles on the contact of solids. Obstacles (smaller than 10µ) are distributed at random on the plates and show, especially in the case of aluminium plates, some `compressibility'.