378 REPORTS ON THE STATE OF SCIENCE.—1912. 
at the same distance in from the end of the stone as in the case of the 
macadam, the stone is immediately tilted up out of the road. The - 
same thing happens when a heavy horse puts his shoe on the end of 
a. stone, or the edge of an iron wheel presses it down. The stone 
being freed from its socket, the road at that point is spoiled, presenting 
a hollow in which water can lodge, and the sides of which can be 
crushed down by the traffic, with fatal result to road efficiency. The 
effect is even worse if round stones with no sharp-edged surfaces are 
used. (Stones shown.) Such stones must work loose and leave a hole 
to be widened and deepened, and filled with water when rain falls. 
Another evil is that too often the camber of the road is made too 
high, it being the practice to pile stones on the centre of the way, without 
making such arrangements as will keep the curve of the road low. The 
result is that drivers, to escape the extra strain on their horses by driving 
along the side of a slope, and to avoid slipping down to the gutter when 
the road is greasy, keep on the very centre of the road, on which two ruts 
are soon formed which gradually get deeper, and in which water lodges, 
with most disastrous effect, the water being splashed out by the wheel, 
and mud being forced up and out by the blow struck when the tire goes 
down into the hollows formed. (Two diagrams shown.) 
Speaking of the blows struck leads me to say that the road made of 
stones with mud in between them is a road in which at every stroke of 
the horse, especially the heavy horse with a heavy iron shoe such as I 
show you (large shoe with calkins shown), shakes and moves the stones 
in the crust many inches below the surface. The same occurs when 
there is any depression into which the wheel goes down with violence. 
The consequence is that the crust becomes unstable, the stones below 
the surface being moved about and their sharp binding surfaces 
destroyed, by which the life of the crust is much diminished. That the 
stones are moved I can demonstrate to you. The Edinburgh Surveyor 
cut out for me a piece of mud-bound—or, as it is incorrectly called, 
water-bound—macadam, and these stones which I show you were taken 
out at a depth of six inches. You will observe that all their angles are 
rounded off, so that they have become of an irregular egg-like shape. 
They have been constantly moved, and they are therefore incapable of 
being bound to form a firm crust, without which no road can stand 
under traffic. 
Such was the state of matters when the power-vehicle was brought 
upon the road. It soon became apparent that the traffic would be very 
greatly increased, that enormous numbers of passenger vehicles and of 
commercial vehicles were being used on the road, doing work which for 
half a century had been done by the railroads. To-day it is impossible to 
dispute the fact that the mechanically-driven vehicle is predominant, 
that the use of horsed vehicles is steadily diminishing, and that on many 
roads where 20 to 50 vehicles passed in the day, 200 or 300 or even 
more traverse the highway. I show you a diagram made from personal 
observation. Counting the passing vehicles till the number of 500 motor 
vehicles was reached, it was found that only 10 horsed vehicles passed 
in the same time. This was during last year. I was so astonished at 
the result that I took a check-count for a few minutes, and found that 
