The word macadamised is, as is well known, derived from one John Loudon Macadam, who in the year 1816 first took up the question of putting broken metal upon a road instead of the boulders previously used.[12] His name, being rather a peculiar one, has been attached to this description of road ever since.
As a matter of fact, the “macadamised” roadways of the present day are constructed after a method introduced by Thomas Telford as an improvement upon Macadam’s principles, and a perusal of the two following specifications will, I think, show that there is not very much difference between the method introduced by Telford and that followed at the present time.
Specification of a Roadway as designed by Thomas Telford more than fifty years ago.[13]
“Upon the level bed prepared for the road materials, a bottom course or layer of stones is to be set by hand in form of a close, firm pavement; the stones set in the middle of the road are to be seven inches in depth; at nine feet from the centre five inches; at twelve feet from the centre four inches; and at fifteen feet three inches. They are to be set on their broadest edges lengthwise across the road, and the breadth of the upper edge is not to exceed four inches in any case. All the irregularities of the upper part of the said pavement are to be broken off by the hammer, and all the interstices to be filled with stone chips firmly wedged or packed by hand with a light hammer, so that when the whole pavement is finished there shall be a convexity of four inches in the breadth of fifteen feet from the centre.[14]
“The middle eighteen feet of pavement is to be coated with hard stones to the depth of six inches. Four of these six inches to be first put on and worked in by carriages and horses; care being taken to rake in the ruts until the surface becomes firm and consolidated, after which the remaining two inches are to be put on.
“The whole of this stone is to be broken into pieces, as nearly cubical as possible, so that the largest piece in its longest dimensions may pass through a ring of two and a half inches inside diameter.
“The paved spaces on each side of the eighteen middle feet are to be coated with broken stones or well-cleaned stony gravel up to the foot path or other boundary of the road, so as to make the whole convexity of the road six inches from the centre to the sides of it, and the whole of the materials are to be covered with a binding of an inch and a half of good gravel free from clay or earth.”
If the above specification, written more than fifty years ago, is compared with one of the present date, it will be seen that there is a strong resemblance between them.
Specification of a Roadway as now executed.
The cross section of the roadway when finished is to be an arc of a circle, with a rise of 1 in 27 from kerb to the centre of the roadway each way.[15] The roadway, when consolidated and finished, to be 12 inches in depth at the gutters and 15 inches at the centre, diminishing gradually from this point right and left to the depth named. The gutters to be 2 feet in width, formed of stone setts 6 inches by 6 inches, and laid in sand, on a firmly consolidated surface of small broken stone or gravel.