In the course of his lecture, he said:—Sometimes it was easy to find the way, but at other times it was extraordinarily difficult, and he would describe certain methods they had for getting over those difficulties; they were not perfect nor were the instruments used perfect, so he hoped that someone there might hit upon improvements arising out of what he was going to say, and, if so, he hoped they would write and tell him all about it.

Suppose we were in the middle of Hampstead Heath on a very dark night and that there were no lamps nor lanterns that one could recognise and we wanted to find our way. One would, of course, suggest that a compass would first be necessary. A night marching compass with a luminous dial was the next step. With these we could find how far one had gone in a certain direction.

So far as is known, the only papers containing reference to the principles of rigid airship design or construction are those delivered by Herr Dornier to the German “ Schiffbantechnischen Gessellschaft ” in 1915 and by Mr. C. I. R. Campbell before the Institute of Naval Architects in 1919. The former paper dealt particularly with the Zeppelin, but while it contains valuable information yet it does not deal with the fundamental principles underlying rigid airship construction.

Further, the figures and estimates that are deduced are based on performances of the earlier Zeppelins and have been substantially improved upon during the war. The present paper is intended to state as far as possible the various principles underlying the design of a rigid airship, in the hope that such information may be of value in the progress of this important branch of aeronautics.