SECTION G.—ENGINEERING. 
THE STABILITY OF STRUCTURES 
ADDRESS BY 
J. S. WILSON, F.C.G.I., Hon. A.R.I.B.A., M.I.C.E. 
PRESIDENT OF THE SECTION. 
THE subject I have chosen appeals to me because I have had to devote 
much time to various aspects of it and, by experimental research have 
endeavoured to contribute something to the solution of some of its 
problems. 
From the engineering point of view, stability is a somewhat dull subject, 
yet the history of its development is of great interest. Instead of trying 
to deal with the subject in a comprehensive up-to-date way, I propose to 
describe some of the more interesting episodes in its history. 
The meaning of stability is not easy to define. In dynamics and 
mechanics we have stability of steady motion and stability of equilibrium, 
of position and of friction. To the civil engineer the word is usually 
applied to the power of a structure to withstand for an indefinite time all 
the loads and forces that may be brought to bear on it. 
As an indication of the wide range covered by my title I may call your 
attention to a few examples. The most stable structure ever built is 
probably the Great Pyramid of Egypt. It consists of large blocks of 
limestone carefully shaped and piled together to the height of 480 ft. on 
a base measuring 830 ft. square. Another instance of a great pile: a pile 
of bricks laid one on another, is a tall chimney such as the celebrated one 
at St. Rollox in Glasgow. This had a height of 435 ft., and at its base a 
diameter of 40 ft. It was pulled down a few years ago after having stood 
since 1842. 
A masonry dam built across a valley to impound water is another form 
of structure the stability of which must be beyond question, as failure 
would lead to disastrous flooding. 
Then we have the arch, the most beautiful and fascinating form of 
construction invented by man. In its simple form we have arches across 
rivers of imposing size and graceful stability, while in cathedrals and other 
great buildings we have it in the groin, dome and buttress. 
~ In each of the above instances, strength and stability depend mainly 
