Investigations have shown that with the addition of Kirsch's supplementary stresses to the elastic expansion and rivet side-thrust, there is a liability to dangerous stress concentration at the edge of the rivet hole. The influence of these edge stresses on the adjacent hole(s) and the plate margin, also requires investigation.

However, since in spite of this disadvantage, riveting is in practice found to be superior to welding, it is evident that the edge stresses must be effectively neutralised by combined elastic and permanent deformation of the material around the hole. At the same time, the unavoidable weakening of plate and hole edges by hair cracks, etc., makes it advisable to pay special attention to the following points :—

1. 1. The initial stresses, in the plates to be joined, should be kept as low as possible.

2. 2. Rivet holes should be accurate and cleanly finished.

3. 3. Rivets should not be too closely spaced.

4. 4. The plate margin should be wide enough to avoid risk of breakdown through stress concentration due to hair-cracks or small notches.

5. 5. The edges of the plates and rivet holes should be reamed to remove hair cracks and local crumbling.

The experiments were carried out in the high speed wind tunnel at Guidonia on three brass spheres of 40, 60 and 80 mm. diameter, supported on rear spindles and on two steel cylinders of 15 and 30 mm. diameter respectively, which passed through the air jet.

Both the total drag and pressure difference between the front stagnation point and a variable point at the rear were measured.

The pressure distribution on similar models which could be rotated and which were provided with pressure holes was also determined.