184 W. M. HAMLET, 
Instance a wooden girder or a pile: it is according to 
specification; satisfactory alike in form, nature and position, 
the timber is sound; it is able to stand the mechanical 
strain, and the stress and torsion expected of it. All this 
has been very carefully thought out in the calculations of 
the engineer, and remembered and provided for by the 
builder. Yet there are other hosts to be reckoned with,’ 
and these are: 
I. Chemical (Electrical) influences. 
II. Mechanical and meteoric influences; the erosion by 
sand, wind and rain, factory-chimney emanations, 
accelerated by expansion and contraction. 
III. Biological influences and animal depredations. 
I feel the subject widens under my treatment and that 
it involves the consideration of three clearly defined divis- 
ions of the subject: the general question of the structure 
of materials, their position in time and space, and thirdly 
their own special environment. ‘To deal adequately with 
these, is more than I can hope for, but I think, we have in 
this threefold summary, all the factors concerned. 
In regard to structure of materials, which is a vast sub- 
ject and involves the consideration of the constitution of 
matter, I would mention that all kinds of matter whatso- 
ever under suitable conditions from the most friable up to 
the hardest steel, carborundum or diamond, are capable of 
easy disintegration and solution in the chemist’s crucible: 
so, conversely, he should know the conditions that deter- 
mine the least amount of chemical action and decay, or in 
other words the conditions of permanence and protection. 
I pass by in review some of the materials used by early 
man: suchas his flints, his diorites, granite and baked clay, 
the bronzes and the marble of the Heyptians, Greeks, and — 
Romans, and come down to the iron of the twentieth — 
century; chiefly for the reason that my attention has been 
