278 Improvement in the Construction of Bridges, &e. 
1st. An immense additional strength may be obtained, with 
much less quantity of plank in the string-pieces, in proportion to 
the strength, stiffness, and durability thereby gained ; especially, 
as double the number of tree-nails pass through all the string- 
pieces which are in the middle of each truss, or between the two 
series of truss-braces, and.thereby secure the splices of the plank 
composing the string-pieces, in a much more effectual manner, 
against their ¢ension strain, which is great, and therefore requires 
the best possible security to counteract it. This manner is 
effectual, even without the aid of iron, to a greater degree thanis 
practicable in any other manner known in practical mechanics. 
2. The great evil, so much complained of in the first mode, by 
all bridge builders, viz. of keeping the trusses straight, or from 
warping, twisting, or leaning sidewise, is by this improvement 
entirely done away; it being more easy to keep the trusses in 
their true position, and have them remain so,. than in any other 
e; becatise, first, the trusses are of greater thickness, and 
therefore less liable to admit of any curve, twisting, or deviation 
from their true position. And secondly, because the trusses ran 
horizontally, they are less liable, even with the same thickuess, 
to get out of their straight and vertical position, than would be 
the case with the arched bridge, which, by rising higher at the 
crown of its arches, gives much greater leverage to its own grav- 
ity, and to the winds, fora deviation from its true position, to 
that of a curved or twisted one, which might impair its strength 
- or safety. 
it may be stated, as it is believed by the patentee, that with 
this last improvement, his mode of construction, for all important 
purposes, is such as to avoid all possible objections of every kind, 
for whatever purpose it may be used; but more especially for 
bridges of very wide spans, as also for railroads and aqueduets, 
which indispensably require great strength, and a level road-way; 
which other bridges would not admit of, to an equal degree, how- 
ever much might be expended in their construction. 
The patentee is aware, that some engineers have by some 
means obtained the opinion, that this improvement, though good, 
and very strong for a proper extent of span, as well as more 
economical than other modes, is not as well suited to very wide 
Spans, as possibly some other mode might be! There could not, 
most certainly, be formed an opinion more erroneous. With 
