538 ON DRAUGHT. 



horizontal, unless the journey be short, or the traffic be only in one direction, 

 and the cart return empty, or unless any other reason render it desirable to 

 compel the horse to exert himself more than he would naturally do ; the traces 

 should then be inclined downward towards the carriage, with an inclination 

 perhaps of one upon four or five, provided always that the horse is capable of 

 continuing the exertion which, by the additional load thrown upon his shoulders, 

 he is thus called upon to make. If, in the same case of low speed, the road 

 be very heavy, or broken and rough, the proportion of draught upon each horse 

 must be lessened by diminishing the load, but the traces should be attached 

 still lower to the carriage, at a slope of one upon three or four, by which much 

 greater power is given to the animal to drag the load over any obstruction. 



At all high velocities, the traces should generally be horizontal. The cases 

 of rough roads or powerful horses may slightly affect this arrangement, as at 

 low velocities, but not in so great a degree. 



We will now proceed to examine the mode in which these conditions are 

 practically to be fulfilled, and the result of the application of the principles which 

 we have laid down, by considering the subject of the vehicles for conveying the 

 weight to be moved. 



Those in present use are boats, as canal-boats, sledges, and wheeled carriages, 

 which last of course include every species of carriage, whether waggon or cart, 

 heavy or light. 



Canal-boats and canals we suspect are gradually going out of use, and will, 

 excepting in some peculiar cases, or unless some great improvement takes place 

 in time, be superseded entirely by railways ; but still it must be many years 

 before this can be effected ; and in the mean time, the produce of the most 

 extensive manufactories in the world, and the supply of immense masses of 

 people, will be transported over these beautifully smooth, level, and noiseless 

 roads ; and, even if their beds were dry, and become the course of railways (an 

 event which may perhaps befall some of them), we must, out of respect for the 

 extraordinary benefits we have derived from their assistance, and the almost 

 incredible effect they have produced upon the commerce and riches of the 

 country, have devoted a few lines to that part of their consideration which bears 

 upon our subject, viz., the draught of canal-boats. 



The great advantage in the transport of goods by water conveyance, is the 

 smallness of the power required. A body floating in water is left so very free 

 in its movements, that motion may be gradually communicated to it by any 

 power however small, at least the limit is very far removed ; but although a 

 very slow movement may thus easily be obtained, the slightest increase of speed 

 causes a very great increase of resistance. 



The resistance to a body moving in a fluid, arises principally from the striking 

 of the particles of the fluid against the front of the moving body, so that if the 

 speed of the vessel be increased, not only does it encounter a proportionably 

 greater number of particles, but also it is struck by each with a force propor- 

 tionate to the velocity, and consequently the resistance is found to increase as 

 the square of the velocity; thus, if the speed of the vessel be trebled, the 

 number of particles, or the quantity of water which it meets in its progress for 

 a certain space of time, is trebled, and the resistance of each particle being also 

 three times as great, owing to the boats striking it with treble the velocity, the 

 united effect is nine times as great ; therefore, if in the first instance it required 

 one pound to draw the vessel, it would now require nine, but nine times the 

 weight or resistance, moved at three times the velocity, will require twenty- 

 seven times the quantity of power in action; consequently, we see that the 

 resistance increases as the square of the velocity, and the power required to be 

 exerted for a given time increases as the cube of that velocity. 



