Trinity Pier of Suspension. S5 
The inner pier is a stone pillar of solid masonry, 6 feet square 
and W feet high. The main bars pass over the top of this pillar, 
similar to the standards erected on the piers. The back stay-bars 
form an angle of 45'’ ; the extremities are sunk about 10 feet be- 
low the surface of the groXind, and secured in hai'd clay by cast 
iron plates, on the principle of a mushroom anchor. The outer 
back-stays are carried in the same angle over the standard of the 
outer pier-head, and are morticed into a rider, which is bolted 
to the piles ; and these riders are backed by spur-shores, to re- 
sist the drag of the bridge. 
The main suspending bars are eye-bolts of S inches, 1 |th and 
l|th inch diameter, being of different dimensions, for the rea- 
sons before mentioned ; and are united end to end, by side-plates 
and bolts of proportional strength. They now become, in ef- 
fect, one entire bolt ; and although separately they are perfect- 
ly straight, yet they all partake of the natural curve of the arch 
between the points of suspension, the dip or versed line of which 
is 14 feet in each division. 
The lowest bars are 3 inches by Jths thick. The ends overlap 
each other by crank-joints, bolted and hesped tight. They are 
supported in a horizontal position by perpendicular straps, passing 
through the joints of the main suspending bars, and the beams of 
the rider are laid across them, and covered with 2 inch plank. 
The butt ends of the beams arei^cased in with a neat cornice and 
blocking, extending the whole length of each division. On each 
side is a wrought-iron railing about 4 feet high ; the perpendi- 
cular straps which support the bridge forming standards for the 
rail. 
The great utility of the Trinity Pier has been already ascer- 
tained : its strength and durability, therefore, become a subject 
of increased importance. 
Agreeably to many hundred experiments which I have made 
with a Machine correctly adjusted, upon the principle of the com- 
mon weighing machine, I have found that it requires a force 
equal to 147,000 lb. to tear asunder a round bolt 1| inches 
diameter, applied in the direction of its length ; but it begins to 
stretch with about f ths of this strain when uniformly supported ; 
and I have therefore proved the main suspending bars, connect- 
ed as they are in the bridge, with 88,200 lb» or about 40 tons. 
