TRANSACTIONS OF THE SECTIONS. 197 
force of three ounces each, would acquire a constant speed of about 
thirty miles an hour. It is also ascertained fromexperiment, that eight 
pounds would draw a ton weight on four three-feet wheels running on 
level rails, and thus that a force of forty pounds would draw the car- 
riage. The following table is constructed from data, by which it is 
found that seventeen-horse power of steam-engine is required to turn 
each mile of wheels, and two-horse power to drive each carriage. The 
power to turn the wheels is neither increased by additional carriages 
nor by acclivities, each carriage added taking only two horse power 
more to carry it along upon a level; and an acclivity of 1 in 180 
doubling, 1 in 90 quadrupling, and 1 in 45 octupling only the tractive 
force, without in any case requiring more than the seventeen-horse 
power to turn the wheels. 
HORSE POWER. 
‘ PASSENGERS. | Per Mile in 2 Minutes. 
Carinae a 
SY CrY Every 2 I U U; U; 
Minutes. || yrinutes. | 12 Hours.|| a Level. | 1in deo. | 1in'90. {~1in45. 
1 40 14,400 19 21 25 33 
2 so | 28,800 || 21 25 33 49 
3 120 43,200 23 29 41 65 
4 160 57,600 25 30 49 81 
5 200 72,000 27 37 57 97 
On Timber Bridges, with reference to their Application to the economical 
construction of Railways. By Mr. Mircue.t. 
About twelve years ago he had erected a bridge across the Spey, con- 
sisting of an arch of 100 feet span; another about six years since of two 
arches of 100 feet span, with stone abutments and piers ; a third across 
the Dee, of five arches of 75 feet span, with timber piers ; besides a 
number of others of smaller dimensions. Ciconomy was the chief ob- 
ject in building bridges of this material. It was found they were one- 
third less expensive than stone ; that across the Dee, with timber piers, 
less than half. The period of duration he found to be from thirty to 
forty years; the accumulated value of the staving being more than 
equivalent to rebuilding the structure. In his opinion, viaducts of this 
material might be beneficially applied in the construction of railways, 
of course being suitably constructed to resist the violent action and 
heavy weights of railway trains. 
Mr. Taylor mentioned that he had that morning received a letter 
from Mr. Enys, stating that Commissioners from the Dutch govern- 
ment had visited Cornwall, to ascertain the duty done by the Cornish 
