148 Mr Buchanan’s Report on the Bridge of Suspension 
put together ; but should this improbability even occur, and 
should the load, for example, of an assembled multitude begin 
to stretch the chains, this circumstance could not fail to be ob- 
served. The sinking of the roadway would signify the ap- 
proach of danger long before any accident could happen : so that 
if the structure be combined, with proper attention and skill, 
the actual breaking of the chains is a contingency which cannot 
take place by any possible concurrence of accidents. 
In such bridges, then, it appears the utmost security is ob- 
tained in the arch itself, by proving carefully the strength of 
every bar or bolt of iron, of which the main chains are com- 
posed, and also of every joint or fastening, by which these de- 
tached bars or pieces are united into one great suspending chain, 
reaching from end to end of the bridge, there passing over its 
supporting pillars, and terminating in the ground, on each side. 
By thus knowing exactly how much each chain will bear, we 
obtain a safe rule for applying such a number as will cover 
every emergency. 
In regard to the towers for supporting the bridge on each side, 
such strong and substantial pillars of stone and iron can be 
erected for this purpose, as to render it impossible that they 
should be crushed under the load they have to sustain. These 
can be founded also on so broad and ample a basis of pile-work 
as to prevent them from sinking : and, lastly, they may be se- 
cured at the bottom by such sufficient fastenings, that they can- 
not be overset by any external force or violence to which they 
are ever likely to be exposed. 
To secure the extremities of the chains, these can be carried 
so deeply under ground, and there bound securely to a platform 
of pile-work, so firmly and deeply rooted into the soil, and so 
heavily loaded with stones or gravel, that the chains themselves 
would be torn in pieces before the load which stretches them 
could either disengage the fastenings, or pull up the piles. In 
all these cases, it is only necessary to know exactly the load 
which is ever likely to be laid on the bridge, or the nature of 
any external violence which may be apprehended, and to guard 
these vulnerable points of the structure, by a degree of strength 
in the several constructions, proportioned to the strain which 
each has to bear. 
