•548 OX DRAUGHT. 



lines to that jiart of tlieir consideration wliicli bears npon our snhject, ^'iz. 

 tlie di-auglit of canal-boats. 



The gTeat 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 fi-ee 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 encounte/a 

 proportionably greater number of particles, but also it is stiTick 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 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 

 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, wdll 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. 



This law of the increase of resistance is modified however by other 

 causes, which have been observed and deeply investigated Avithin "the last 

 ?tiw years, and which produce such an effect, that with boats of a pecuhar 

 form a diminution of resistance actually occurs at a certain increased 

 velocity, and very high rates of speed, such as even 10 or 12 miles per 

 hour, have been attained. There are also some small sources of resistance, 

 such as the friction of the water, which do not increase in the ratio above 

 named, but at moderate velocities the rule apphes, and as yet no means 

 have been discovered by which, with the present dimensions of canals and 

 their locks, larger quantities and weights can be conveyed at any but very 

 low rates of speed. The draught of an ordinary canal-boat, at the velocity 

 of 2^- miles per hour, is about ttq-o of i^s weight, that is to say, a canal-boat, 

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

 tioned, by a force equivalent to 80 lbs., being -^^-^ part of the load. This 

 is fouaid 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 

 applpng the power, could be removed, the effect might be raised 100 lbs., 

 or 120 lbs. of traction, and consequently the load moved would then be 40 

 or 50 tons; this is an increase well woi'thy 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 



