Reformation respecting Rail- Roads. 105 
view of preventing them from cutting grooves in the wheels, and 
that breadth appears to answer well for the heaviest weights 
likely to be permitted on rail-roads. 
The strange form of a rail-road, consisting of a single line of 
rails, supported on upright pillars, proposed by Mr Palmer, and 
recommended by Mr Tredgold, will, I suspect, be found appli- 
cable to few situations. It differs from others, in requiring not 
only room in breadth and height, but also a clear space of some 
feet below the rail. Thus, it cannot approach the surface of the 
ground without having a trench cut to receive it ; and to se- 
cure a level line, must require either very high pillars in the 
valleys, or deep excavations through the hills. If it be not des- 
titute of curves, the motion on it must be slow and regular, else 
the tangential force of the load will derange the structure ; and 
if the pillars be inclined towards the centre of curvature, to 
counteract the effect of one velocity, that inclination will suit 
no other. If a continuous chain were attached to it, as Mr 
Tredgold proposes, it would meet with a very serious obstacle 
on all roads crossing it ; for, except they should go over it by a 
bridge, it must proceed at a very expensive height above them, 
as it would then be impossible for a carriage to go through it. 
Mr Wood has made the nearest approach to the complete 
elucidation of the data necessary to determine the resistance 
upon rail-roads, and the power requisite to overcome it. The 
experiments made by Mr Tredgold for this purpose, do not ap- 
pear to be of much value, and in his book they are narrated 
too vaguely, to lead the reader to any decisive conclusion. In 
those which he has described, for the purpose of shewing the 
proportional resistances with different loads, and different wheels, 
the weights which produced the motion seem to have been omit- 
ted in determining the mass moved ; and the real resistance, in- 
dependent of the accelerative force of the moving weights, is not 
calculated at all. In the two experiments, from which he de- 
duces the real amount of the friction at the axle of the carriage, 
the proportion of the gravitating force, employed in accelerating 
the revolution of the wheels, was probably of sufficient amount 
to require alteration. Mr Tredgold remarks, that “ He a- 
voided the smoothness and accuracy of workmanship,” in pre- 
paring his model, “ which could not be adhered to in machines 
