PRESIDENTIAL ADDRESS. 25 
painted from year to year. Messrs. Burr, Cooper, and 
Morrison reported that the cost of the Hudson River Bridge 
would be £7,073,400, if the suspension type were adopted, 
and £10,225,600 for a cantilever of the same capacity. 
The steel wire used in the modern suspension bridge 
has a tensile strength of 220,000 lbs. per square inch, and 
with such wire it would be possible to build a bridge suit- 
able for the heaviest railway traffic of 4,000 feet span 
with perfect safety, but since the length of the span 
attainable depends upon the weight and strength of the 
material used in the construction, it follows that if larger 
spans are built in the future, the strength of the material 
must be considerably increased. 
It is difficult to predict what improvements may be 
made in the future, and no doubt many surprises await us 
during the next 25 years; but the scientific and practical 
work of the metallurgist and the engineer may render 
practicable the use of some alloy, such as nickel and iron, 
having greater strength and elasticity than modern 
structural steel. The physical properties of the alloys of 
nickel and iron are well understood, but the material is 
. very costly, and there is some difficulty in rolling plates of 
nickel steel containing the percentage of nickel most suit- 
able for bridgework. 
The Design and Construction of Foundations.—Gene- 
rally the methods adopted have been more or less used for 
a considerable time; but the chief developments in this 
branch consist in the application of the freezing process 
in sinking shafts and foundations, mainly in the United 
States, and in the method of open dredging in such cases 
where the ordinary pneumatic process would be unsuit- 
able, in consequence of the effect on the workmen at 
great depths, necessitating correspondingly great pressures 
of air. 
