ON DRAUGHT. 



42: 



The resistance to a body moving in a fluid arises principally from th«* 

 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 proportionate to the velocity, and consequently the resistance 

 is found to increase as the square of the velocity; thus, if the speed of tlie 

 vessel be trebled, the number of particles, or the quantity of water wliich it 

 .neets in its progress for a certain space of time, is trebled, and the resist- 

 ance of each particle being also three times as great, owing to the boat's 

 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 tv/enty-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. 



There are some other causes of resistance, which do not vary in this 

 proportion, but at moderate velocities ; and, in all ordinary cases, this may 

 be considered as a tolerable approximation to the real law of the increase, 

 and shows at once the impossibility of using water conveyance where speed 

 is required. The draught of an ordinary canal-boat, at the velocity of 2i 

 miles per hour, is about gi^- of its weight ; that is to say, a canal-boat, with 

 its load weighing 33 tons, or 73,920 lbs., is moved at the rate mentioned, 

 by a force equivalent to 80 lbs., being gig part of the load. This is found 

 by Mr. Bevan to be the result upon the Grand Junction Canal, and a force 

 of traction of 80 lbs. is here found to be equivalent to a horse-power. The 

 average power of an ordinary horse is certainly rather more ; and in the 

 commencement of this paper we mentioned this as an instance of a small 

 effect being produced, most probably owing to the peculiar application of 

 the power. We believe it to be the case, and think it likely that, if the 

 disadvantages before alluded to, arising from the mode of applying the 

 power, could be removed, the efl^ect might be raised to 100 lbs. or 120 lbs. 

 of traction, and consequently the load moved would then be 40 or 50 ton.? ; 

 this is an increase well worthy of consideration. 



We now come to the consideration of the means of transport employed 

 on land. These are sledges, rollers, and wheel-carriages. The order in 

 which they are here mentioned, is, probably, that in which they were 

 invented or first employed. A sledge is certainly the rudest and most 

 primitive form of vehicle ; the wheeled-carriage, and even the placing the 

 load itself upon rollers, is the effect of a much more advanced state of the 

 mechanical arts, and is, probably, of much later date than the sledge. 



When man first felt the necessity, or the desire, of transporting any 

 article from one spot to another, he doubtless endeavoured to lift or carry it: 

 if it proved too heavy for him to carry, he would naturally endeavour to 

 drag it. Here frequent experiments would soon show him how much less 

 labour was required to drag a body with a smooth surface in contact with 

 the ground, than when the contrary was the case; and if the body to be 

 moved did not itself present a smooth surface on any of its sides, but was, 

 on the contrary, rough and angular in all directions, he would naturally 

 be led to interpose between it and the ground some plane surface, which 

 should prevent the angles and projections of the body from entering the 

 ground and impeding the progress; and we may presume that sledges were 

 thus very early brought into use. When attempting to transport still heavier 

 masses, the accidental pressure of round stones, or a piece of a timber, may 

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