PRESIDENTIAL ADDRESS. 23 
1. The invention of the various processes for the manu- 
facture of cast iron, wrought iron, and structural 
steel. 
2. The experiments made in order to determine the 
physical properties of the material of construction in 
the first instance by such men as Telford, Rennie, 
Rondelet, Tredgold, Dufour, Sequin, Hodkinson, 
Stephenson and Fairbairn, and more recently by the 
elaborate investigations and researches conducted in 
engineering laboratories provided with special forms 
of testing machines and apparatus for accurately 
measuring stresses and the deformations produced by 
them. 
3. To the mathematical investigations, aided by experi- 
mental researches on elasticity and the calculation of 
stresses and deformations in structures by such men 
as De Saint Venant, Claperon, Mohr, Winkler, Bach, 
and Castigliano. 
It is interesting to note that Robert Stephenson actually 
built the Menai Bridge in 1846-7, which consists of a con- 
tinuous box girder of three spans, each 466 feet, large 
enough for a train to pass through it, while Claperon’s 
method of calculating the stresses in such girders was not 
published until eight years later. 
The art of the bridge-builder, both in its theoretical and 
practical aspects has gradually become most precise and - 
exact in every particular, and to-day there is no branch of 
engineering where science and experience has been so 
completely united, or where greater success has been 
achieved in economy of material, manufacture, and 
efficiency. The first realiron bridge was built by Abraham 
Darby in 1776, of cast iron, and cast iron was used in the 
compression members of trusses in America as late as 1875; 
the use of structural steel, such as we understand it to- 
