Construction, Cost, Repair, and Mancif/ement. 395 
the harder and more level the surface, and the more solid the 
foundation, the less the tractive power required. 
T • •»! Greatest in- 
Limiting ciination which 
'should be given 
I resistance. ^ ^ 
Well-laid pavement I 0*oO 1 in 68 
Broken stone surface, on a bottom of rough pavementjl j.jj i i in 49 
or concrete / 
Broken stone surface laid on old flint road 1*40 1 in 34 
Gravel road 1 3-45 ' 1 in 15 
From experiments made by Sir John MacNeill and others, it 
has been ascertained that the resistance on various kinds of roads, 
is as follows : — r ■ n ^ 
^^^^^ - Force in Pounds 
required to move 
a Ton. 
lbs. 
On a railway 8 
On a well-made pavement 33 
On a road made with six inches of broken stone of great hard- 1 
ness, laid either on a foundation of large stones set in the f 
form of a pavement (Telford's plan), or upon a bottoming of | 
concrete 
On an old flint road, or a road made with a thick coating of] 
broken stone laid on earth 
On a road made witli a thick coating of gravel, laid on earth .. 147 
46 
65 
The following general rules have been laid down by Mr. 
Morin, after experiments made at the expense of the French 
Government. 
1st. The traction is directly proportional to the load, and in- 
versely proportional to the diameter of the wheel. 
2nd. Upon a paved or hard Macadamised road, the resistance 
is independent of the width of the tire, when it exceeds from 
■3 to 4 inches. 
3rd. At a walking pace the traction is the same under the 
same circumstances for carriages with springs and without them. 
4:th. Upon hard Macadamised, and upon paved roads, the 
traction increases with the velocity ; the increments of traction 
being directly proportional to the increments of velocity above 
the velocity of 2^ miles per hour. 
The equal increment of traction thus due to each equal incre- 
ment of velocity is less, as the road is more smooth and the car- 
riage less rigid or better hung. 
bth. Upon soft roads of earth, or sand, or turf, or roads fresh 
and thickly gravelled, the traction is independent of the velocity. 
Gth. Upon a well-made and compact pavement of hewn 
