490 TRANSACTIONS OF SECTION G.—PRESIDENTIAL ADDRESS, 
Section G.—ENGINEERING. 
PRESIDENT OF THE SxctTIoN.—Professor E. G. Coxer, M.A., D.Sc., 
M.Inst.C.EH. 
The President delivered the following Address at Sydney on Friday, 
August 21 :— 
Tue subject of stress distribution in materials, which I have chosen for this 
address, is not one which an engineer can claim as his peculiar province, for it 
has been and still is a fruitful field of investigation for the mathematician, the 
physicist and the geologist, and has always been so since the commencement of 
scientific inquiry ; indeed, it must have been the source of speculation and con- 
troversy ever since mankind emerged from a primitive state, and began to fashion 
dwellings, weapons, and tools from the materials at command. 
The development of architecture from the earliest dwellings of savage races 
to the great temples of Egypt and Greece, the bridges and aqueducts of the 
Romans, and the medieval buildings of Europe, all bear witness to the accumula- 
tion of practical knowledge of the properties of materials and of the stress dis- 
tribution in structures, which we cannot fail to admire, although we know far 
too little of the way in which these ancient structures were planned and con- 
structed. The magnificent arched and domed buildings of the Roman period, and 
the stately cathedrals of later times with their wealth of architectural form— 
tower and spire, flying buttress and vaulting—all show how considerable was the 
practical knowledge of stress distribution possessed by the master builders who 
planned and carried out these great structures. We, who inherit these buildings 
as a precious legacy of bygone ages, have at our command far greater resources 
in the accumulated knowledge of centuries of scientific discovery and invention, 
and can build more complex structures—great bridges of steel, towering frame- 
works covered by a thin veneer of masonry, and floating arsenals of the most 
bewildering intricacy. All these we can show to our credit as the result of the 
steady increase of scientific knowledge applied to practical ends, but, even now, 
knowledge of the stresses which come upon these complex structures and 
machines is relatively small. Scientific investigations of engineering problems of 
stress still lag behind constructive ability, and defective knowledge is obscured 
more or less by approximate theories and buttressed by factors of safety, which 
serve in one instance perhaps, but show in others that they have merely given a 
sense of fancied security with no real basis, and are more properly factors of 
ignorance, to be discarded at the earliest moment. Who, for example, can say 
with certainty what is the stress distribution throughout the compression members 
of a great bridge, built up of complicated steel shapes and plates, united by 
stiffening angles, gusset plates, and innumerable rivets? There is probably good 
reason for the belief that a great strut is relatively weaker than a small one, 
when both are designed according to the same approximate formule now used in 
current practice, and engineers are unwilling to take the responsibility for such 
members in a great structure, without providing a very ample margin of safety 
to cover the contingencies arising from lack of precise knowledge of the strength 
of these members. So numerous are the problems which arise in the design and 
construction of machines and structures, that it is perhaps not unprofitable to 
