7. It appears by this table that no regular proportion has been observed between the breadth of the wheels, the weight of the load and the number of horses; in the fifth column the sum of the pressure on the wheel decreases pretty gradually as the wheels become narrower; but in the sixth column, where the breadth of the wheel is taken into the account, the intensity of the pressure on every inch of the surface that is rolled, is increased as the wheels become narrower, which seems contrary to all reason,

8. With the nine-inch and the six-inch wheels, when they roll a double surface, the weight of the load is considerably increased, although the resistance to the progress of the wheels, and the labour of the cattle, with the same load, is increased by rolling the double surface.

9. If the roads be in good order, the double rolling is of no use; if they be soft and compressible, the resistance becomes greater, as the surface that is rolled is broader; and it is generally supposed, that the resistance in rolling the double surface is the same as with the single; but it ought to be remembered that with the single surface the nind wheels run in the paved track of Uu 2

the

the front wheels, but with the double surface every wheel has to compress and level its own track.

10. It is much better to increase the breadth of the cylindrical wheels, than to make the front and hind wheels of the same carriage to roll double surfaces; the intensity of pressure on the surface of the road is diminished by increasing the breadth of the wheels, but not by rolling a double surface.

11. The advantages of rendering the intensity of the pressure of the wheels of all carriages as nearly equal as may be practicable, would be of the next greatest importance to the introduction of the cylindrical wheel.

12. Let us suppose a three inch wheel under a load of 3 ton running in the track made by a 16-inch wheel with the load of eight ton; the intensity of the narrow wheel 650 lb.; that of the broad wheel, in whose track it runs, is only 280 lbs.; the narrow wheel will therefore cut up the bottom of the broad track, and meet with much more resistance than if it made no such impression; the resistance to the next wheel that follows in the same path is increased by the breaking up of the path; and the smooth surface of the broad track being cut open, it admits water, and introduces all the bad effects of wet seasons and subsequent hard frosts; all which evils might be avoided by having the intensity of the pressure of the narrow wheels only equal to, or something less than, that of the broad wheel; the narrow wheel would in that case roll with great facility in the path of the broad wheel, without making any impression, or in any respect damaging the track in which it runs.

13. And if all wheels were made of as equal intensity as, circumstances, will permit, they would mutually roll

in the tracks of each other, without any other effect than each repairing the path of any accidental damage which it may have received since the last wheel passed, the road will become more and more consolidated, its surface more close and impervious to water; there will be no dragging or grinding of conical wheels, no means of converting the best material into dust in summer, or into sludge in winter; there will then remain no other cause of damage to the roads except the pedestrian exertion of cattle.

14. The intensity of the pressure of the wheels may be regulated by maintaining a regular proportion between the weight of the load and the breadth of the wheels; it is nevertheless adviseable to take the number of cattle into the account, and by that means it would seem that the intensity of the pressure might be preserved sufficiently equal with the cylindrical wheels, without the controul of the weighing-engine, by observing a regular proportion between the number of horses and the breadth of the wheels.

15. The following table, therefore, is so constructed as to give a regular proportion between the number of horses, the breadth of the wheels, and the weight of the load; and as two horses are the fewest that can be employed in a four-wheeled waggon, we begin with that number, and proceed regularly to eight; and taking the average of the weight drawn by each horse, according to the Act of the 13th of Geo. III. we find it 16 cwt.; and assuming that as the weight to be drawn by each horse, according to the new regulation also, the weight of the load is thus determined by the number of horses, allowing 16 cwt. to each; and the breadth of wheel that is allowed to each horse is determined by the six

1

teen

teen-inch wheel drawn by eight horses, which gives two inches of breadth to each horse.

. 16. And by allowing 16 cwt. for each horse, the weight of the load is determinable; and by giving two inches for each horse, the breadth of the wheels is ascertained for any number of horses; and thus the intensity of the pressure of the wheels of all carriages may be determined and kept nearly equal to each other, by maintaining an uniform proportion of the load, and the breadth of the wheels, with the number of horses that draw the waggon, &c.

17. And the following table exhibits at one view the breadth of the wheels, and the weight of the load, for any number of horses from two to eight, to give the same intensity of pressure with each.

the intensity of the pressure of the wheels of all carriages are equal, or nearly so, the tracks of all wheels will be equally deep; and since the wheels are all cylindrical, and the axles straight, every wheel that runs in the track of another will apply its whole breadth as flatly to the bottom of the former track as the wheel

that

that formed it, and having the same intensity of pressure, it cannot disturb the parts that are in contact, nor prevent their cohesion or induration, nor produce any other effect on the former track, unless rendering the consolidation more perfect, and the surface more close and impervious to water, and compressing and uniting any loose or broken particles that may have fallen into the track since the last wheel had passed.

20. And as in the course of the traffic the same carriage will sometimes lead and sometimes follow, no inconveniency or interruption will take place in the uniform system of consolidation and amelioration by that alternate precedency; and it does appear, from what has already been said of the 3-inch wheel rolling in the track of the 16-inch wheel, that the narrow wheel shouldnever have a greater intensity of pressure than the broad wheel, in order that it may run in the broad track without cutting or damaging it.

21. It has been suggested (14) that the controul of weighing engines might be rendered unnecessary, by observing a regular proportion between the number of horses that draw the carriage, and the breadth of its wheels.

22. When conical broad wheels were used, the difficulty of drawing the carriage, and the damage that was done the roads, were increased, as the intensity of the pressure on the surface; and although that intensity was diminished by increasing the breadth of the wheels, the dragging of its rim was so much increased by increasing the breadth, that every addition to the weight of the load became doubly hurtful to the road, and the check of the weighing engines under those circumstauces became necessary.

23. But