Mr Buchanan on the Strength of ‘ Materials. 155 
portion of the different parts. In our furniture, also, and other 
articles of domestic use, the same sort of improvement has taken 
place ; and here it is of consequence to attend to the principles 
of strength, not merely from economy and convenience, but as 
it may contribute to the neatness and tasteful design of the 
work. Consider, again, our wheel-carriages, and compare the 
unwieldy machines of former times, with the light and elegant 
vehicles of the present day. This improvement has also arisen 
from a judicious application of the principles of strength. 
In public works we remark numerous instances to the same 
effect ; and in these cases the matter becomes of still greater 
importance, from the large scale on which many of these works 
are conducted. The construction of bridges presents an eminent 
example ; and here again we have a remarkable contrast between 
ancient and modern practice. Alarmed by the natural instabi- 
lity of the semicircular arch, our ancient builders appear to have 
sought security in the narrowness of their spans, and in the in- 
ordinate thickness of their piers. This plan, however, by ob- 
structing the water-way of the river, led to a new evil, which 
frequently proved the destruction of the works ; the rapid cur- 
rent of the waters, deepening their channel, undermining the 
piers of the arches, and thus sapping the foundations of the 
whole structure. The piers, therefore, were gradually reduced 
in size, and the spans of the arches enlarged, though with slow 
and cautious steps, as the principles of their equilibrium became 
better understood. A vast saving of material has been the con- 
sequence of these improvements, together with a lightness and 
boldness of design, which, in the more modern works, conduces 
greatly to the imposing effect of these noble structures." Much, 
however, remains still to be done, in following out the same prin- 
ciples ; and when we compare the vast mass and solidity of many 
of these works, with their actual strength, and the strains which 
they have to sustain, it will appear that we are yet far from ha- 
ving attained that due proportion of strength to stress, which 
the nature and properties of the arch admit of ; that exact accom- 
modation of resistance to its corresponding pressure which marks 
the combined perfection of science and art. Cases of such mag- 
nitude, and involving such important interests, require, no doubt, 
extreme caution, and the most deliberate inquiry, as to every un- 
