drawing the boat at this increased speed, are found to perform their work better, the resistance to their progress having become less; and the more the velocity of the boat is thus increased, the less resistance she meets with, merely having to cut the still water instead of the wave. It is a curious fact, that the wave produced by the approach of a slow canal boat is often observed at the distance of a mile, and upwards, along the canal, before the arrival there of the boat. But in the case of the high wave being raised by the Paisley canal boat, it is customary to stop the boat, and after it has subsided to start again at a greater velocity. When the boat When the boat is to be stopped for any purpose, as her speed decreases the wave rises in proportion, and washes over the banks, until the motion of the boat becomes so small as to produce none. The discovery is doubtless a very important one, and, if turned to account, is likely to produce a material alteration in the rate of transport on canals. It was not known until these experiments were made, that if a boat, from a state of rest, was dragged along a canal, in proportion as her speed increased to a certain limit, that the power required was greater but that, if she were started at, and preserved a speed exceeding the same limit, the power required would be less, and would decrease as her velocity increased. In fact, from a certain velocity there seems to be no limit to the rate at which a boat, as far as animal power can be applied, may thus pass through the water; and as the rate increases, the power required decreases. On this principle it is, that the boats on the Paisley canal, with ninety passengers in them, are drawn by horses at a speed of ten miles an hour; while it would kill them to draw the same boat along the canal at six miles an hour. A boat might indeed travel fifteen or twenty miles an hour easier than at six miles. The former of these velocities has already been attained by Mr. Grahame, along a distance of two miles, and is considered by him safer both for the boat and the canal.

As a proof of what may be done by this method of carriage, Mr. Grahame states that he has performed a voyage of fiftysix miles along two canals in six hours and thirty-eight minutes, which included the descent of five, and the ascent of eleven locks, the passage of eighteen draw-bridges where the trackingline was thrown off, and sixty common bridges, besides a tunnel half a mile long; all, of course, producing some delay. The boat which performed this was sixty-nine feet long, and nine broad, drawn by two horses, and carried thirty-three passengers, with their luggage and attendants.

These facts furnish great encouragement to canal companies, to improve the construction of their boats and the speed on their

canals; and thus, probably, in some positions, supersede the necessity of rail-roads.

Mr. Macneill, the assistant engineer upon the Holyhead road, under Mr. Telford, in the course of his examination before a committee of the House of Commons, on steamcarriages, rail-roads, &c. gave the subjoined curious information.

Well made roads, formed of clean hard broken stone, placed on a solid foundation, are little affected by changes of atmosphere; but weak roads, or such as are imperfectly formed with gravel, flint, or round pebbles, without a bottoming of stone, pavement, or concrete, are much affected.

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On the generality of roads, the proportional injury from the weather and traffic is nearly as follows. When travelled by fast coaches: from atmospheric changes 20; coachwheels 20; horses' feet 60 = 100. When travelled by wagons: atmospheric changes 20; wagon-wheels 35.5; horses' feet 44.5 100. Has ascertained, from a number of observations, that the wear of the iron tire of fast-going coachwheels is, compared with that of the shoes of the horses which draw them, as 326.8 to 1000, or as 1 to 3-4ths nearly; and infers that the comparative injury done by them to roads is nearly in the same proportion. In the case of slow-going carriages and horses the proportion is as 309 to 360, or as 1 to 1.16, or nearly 1 to 14. The tire of the wheels of the fast-going coaches last from two to three months, according to the weather, the workmanship, and quality of iron; about 20 years ago, it did not last seven days on an average. Coach-horse shoes remain in use about thirty days; wagonhorse shoes about five weeks on an average. Where roads are weak, and yield under pressure, the injury caused by heavy wheels is far greater than on solid firm roads.

It was found, in one instance, that the wear of hard stone, placed on a wet clay bottom, was four inches, while it was not more than half an inch when placed on a solid dry foundation. On the Highgate archway road, the annual wear is not more than half an inch in depth. To the same gentleman we owe the following useful table.

TABLE V.-The general Results of Experiments made with a Stage Coach, weighing, exclusive of seven passengers, 18 cwt., on the same piece of road, on different inclinations, and at different rates of velocity, furnish the following statement.

CHAPTER XV.

ACTIVE AND PASSIVE STRENGTH.

SECTION I.-Active Strength, or Animal Energy, as of Men Horses, &c.

1. THE force obtained through the medium of animal agency evidently varies, not only in different species of animals, but, also, in different individuals. And this variation depends, first, on the particular constitution of the individual, and upon the complication of causes, which may influence it; secondly, upon the particular dexterity acquired by habit. It is plain, that such a variation cannot be subjected to any law, and that there is no expedient to which we can have recourse, but that of seeking mean results.

Secondly, the force varies according to the nature of the labour. Different muscles are brought into action in different gestures and positions of an animal which labours; the weight itself of the animal machine is an aid in some kinds of labour, and a disadvantage in others: whence it is not surprising that the force exerted is different in different kinds of work. Thus the force exerted by a man is different, in carrying a weight, in drawing or pushing it horizontally, and in drawing or pushing it vertically.

Thirdly, the force varies according to the duration of the labour. The force, for example, which man can exert in an effort of a few instants, is different from that which he can maintain equably in a course of action continued, or interrupted only by short intervals, for a whole day of labour, without inducing excessive fatigue. The former of these may be called Absolute Force, the latter Permanent Force. It is of use to become acquainted with them both, as it is often advantageous to avail ourselves sometimes of the one, sometimes of the other.

Lastly, the force varies according to the different degrees of velocity, with which the animal, in the act of labouring, moves either its whole body, or that part of it which operates. The force of the animal is the greatest, when it stands still; and becomes weaker as it moves forward, in proportion to its speed; the animal acquiring, at last, such a degree of velocity as renders it incapable of exerting any force.

2. Let be a weight equivalent to the force which a can exert, standing still; and let v be the velocity with which,

if he proceeds, he is no longer capable of exerting any force : also, let F be a weight equivalent to the force which he exerts, when he proceeds, equably, with a velocity v.

Then F will be a function of v, such that, 1st, it decreases whilst v increases; 2dly, when v 0, then F = ; 3dly, when v V, F = 0.

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3. Upon the nature of this function, we have the three following suppositions.

(1-2). (Bouguer, Man. des Vais.)

1. F = • (1.

2. F = 4

3.

F = ?

(1–2). (Euler, Nov. Comm. Pet. tom. III.)

(1 — 2-) ̊(Ib. tom. VIII ; and Act of Rowers.)

4. Coroll. 1. The effect of the permanent force being measured by the product F v, the expression for the effect will be one of the three following, accordingly as one or other of the suppositions is adopted.

5. Coroll. 2.

To know the weight with which a man should be loaded, or the velocity with which he ought to move, in order to produce the greatest effect, we must make d. F v = 0. Whence we shall have

6. Coroll. 3.

And the value of the greatest effect will be,

according to the 1st hypothesis. ... v: