162 Mr. Town’s new mode of Bridge-building. 
sides of wood towers, steeples, &c. &c. of public buildings, 
as it requires nothing more than common planks instead of 
long timber—being much cheaper, easier to raise, less sub- 
ject to wet or dry-rot, and requiring no iron work. 
Some of the advantages of constructing bridges accord- 
ing to this mode are the following : ; 
1. There is no pressure against abutments or piers, as 
arched bridges have, and consequently perpendicular sup- 
ports only, are necessary ; this saving in wide arches is very 
great, sometimes equal to a third part of the whole expense 
of the bridge. 
2. The shrinking of timber has little or no effect as the 
strain upon each plank of the trusses, both of the braces 
and string-pieces, is an end-grain strain or lengthwise of the 
ood. 
3. Suitable timber can be easily procured and sawed at 
common mills, as it requires no large or long timber—de- 
fects in timber may be diseqvered, and wet and dry rot pre- 
vented much more easily than could be in large timber. 
4, There is no iron work required, which at best is not 
safe, especially in frosty weather, 
5. It has less motion than is common in bridges, and 
which is so injurious and frequently fatal to bridges—and. 
being in a horizontal line, is much less operated upon by 
winds. . 
6. A level road-way is among the most important advan- 
tages of this mode of construction. as 
7. The side-trusses serve as a frame to cover upon, and 
herenvaere any extra weight of timber, except the cover- 
ing itself{—and the importance and economy of covering 
bridges from the weather, is too well understood to need re- 
commendation after the experience which this country has 
ing the connexion, weakens the whole superstructure. 
. The great number of nearly equal parts or joints into - 
which the strain, occasioned by a great weight ‘upon the 
bridge, is divided, is a very important advantage over apy’. 
