ON DRAUGHT. 533 



full beuefit of it, as well as of any iucreased exertions of tlie animal, is felt 

 and is applied solely to di-agging the load. 



Not so with a locomotive steam-engine, because, beyond the power 

 necessary to perform the work of dragging the load, a large additional 

 power must be jorovided to move the engine itself. In other words, if 

 an engine of ten-horse power be capable of dragging a certain load, the 

 weight of this engine forming a portion of the load to be moved, a corre- 

 sponding portion of the power is unprofitably absorbed in moving it, and 

 the excess, or remaining power, is alone available for useful purposes, and 

 can alone be compared to the animal or horse-power. Now, if the draught 

 is augmented, as we have just supposed, by any sand, dirt, or roughness of 

 the road or any other impediment, the force required to move the useless 

 weight (of the engine) is proportionally increased ; it may even, as we 

 have stated, be doubled or trebled ; and the whole power of the engine 

 remaining the same, the surplus or remaining portion is considerably 

 diminished, and that at the very moment when, as before stated, it pro- 

 duces only one-half or one-thii'd the effect. 



Moreover, if at any part of the road a power equal to twenty horses is 

 required, the engine, as regards its construction, must be a 20-lioi'se 

 engine. It is erroneous to suppose that a steam-engine, because it is a 

 high-pressure engine, can therefore, as occasion requires, be worked for 

 any length of time beyond its nominal power, by merely raising the steam. 

 Every part of a machine is calculated and arranged for a certain pressure 

 and corresponding power, and that is the real power of it. It is optional 

 to work at or below that power, but, if below, it will be to a disadvantage, 

 as the bulk and weight of the machine will be as great as if it were always 

 worked to its full extent, and both have to be carried over all those parts 

 of the road where a far less power would be sufficient. The velocity of 

 the carriage might indeed be increased, while travelling on the good and 

 level portion of the road ; but these alternations in the speed and power 

 caim.ot be efiected without a considerable degree of complexity, weight, 

 and expense in the machinery ; and, as we are confining ourselves to the 

 consideration of the case where velocity is not required, and might even be 

 an inconvenience, the excess of power will be wasted. 



These objections to the use of mechanical power, in certain cases, are 

 pointed out, not as being insurmountable obstacles to the use of machinery, 

 but as serious difficulties which, in practice, have not yet been overcome. 

 In fact, there is not at present any practical substitute for horse-power on 

 common roads, and, as far as the pubhcis concerned, nothing has yet been 

 done. We, therefore, must consider them as objections remaining to be 

 overcome ; and we are compelled to draw the conclusion, that, at the pre- 

 sent moment, animal power (always confining ourselves to the question of 

 the economical transport of heavy goods upon common roads) is superior 

 to any mechanical agent, and that beasts of draught, and particularly the 

 horse, although the most ancient, still remain the most advantageous 

 source of power. 



Long experience has pointed out various modes of applying animal 

 power ; but it is fi-equently ill directed, owing to the want of an adequate 

 knowledge of the mechanical structure of the animal, and the manner in 

 which he exerts his strength. 



In the most powei'ful steam-engine, if too great a resistance be applied, 

 or practically speaking, if we attempt to make it do more work than it is 

 calculated for, there is an immediate loss of power, in consequence of the 

 diminution of velocity caused thereby ; and if we continue to oppose a still 

 greater resistance, we reach the point at which it is unable to overcome 

 it, and it ceases to produce any effect. Again, a very small obstacle may 



