A system of external forces on the structure of a rigid airship can be analysed into two or more of the component systems due to

1. 1. W. The Weights of the members of the structure and the weights of the masses carried by it;

2. 2. L. The Lift and pressure of the gas;

3. 3. A. The Aerodynamic forces consequent on the relative motion of the airship and the air;

4. 4. T. The Thrusts of the airscrews;

5. 5. R. The Reactions due to either the mooring arrangements, the hauling-in guys, the supports used in the shed, or handling on the ground.

As these component systems, though restricted by their interdependence, are individually variable, a very large number of complete systems is represented by the possible combinations and variations that can occur. It becomes necessary, therefore, for the purposes of design, to attempt to limit the number of combinations to be considered, and to restrict the variations of the components, but in such a way that the structure designed to carry the resulting systems with adequate factors of safety, shall be able to carry any other possible system with an appropriate factor of safety.

In the July Journal a number of figures from the reprint of the above paper read before the Institution of Automobile Engineers in March, 1917, were unfortunately omitted. The figures are printed below. In the reprint of the paper by Signor V. Isacco (Reprint No. 43) these figures have been placed in their proper position in the text.