ON DRAUGHT. 405 



force which, if the rope were passed over a pulley, would raise 100 lbs., 

 the force of traction of the horse is in this case 100 lbs. Spring steel- 

 yards being now commonly in use, we may be permitted to refer to them 

 as atlbrding another clear exemplification of our meaning. In pulling ai 

 a steelyard of this description, whether the force be exerted horizontally 

 or vertically, the index will, of course, show the same amount ; and con- 

 sequently, if the strength of the horse be measured by attaching the traces 

 to one of these steelyards, the number of pounds indicated on the dial will 

 be the exact measure of the strain the horse exerts, and the amount of 

 strain is called his "force of traction." 



Having fixed as nearly as possible the meaning of these terms, which 

 will frequently occur in the course of our progress, we shall proceed to the 

 division of the subject. 



It is evident that there are three distinct agents and points of considera- 

 tion in the operation of draught, which are quite independent of each 

 other. They are — First, the moving power and the mode of applying it; 

 Secondly, the vehicle for conveying the weight to be moved ; Thirdly, the 

 canal, road, or railway, or what may be generally termed the channel of 

 conveyance. 



All these individually influence the amount of draught, and require 

 separate consideration ; but the mode of combining these different agents 

 has also a material effect upon the result: consequently, they must be 

 considered in relation to each other; and to obtain the maximum useful 

 effect, with the greatest economy, in the employment of any given power, 

 it is evidently necessary that these different agents should not only each 

 be the best adapted to its purpose, and perfect to the greatest possible 

 degree, but also that they should all be combined to the greatest possible 

 advantage. 



We shall proceed at once, then, to examine the different agents now 

 employed, the modes of applying them, and the proportionate effects 

 produced. 



And, first, with regard to the species of moving power: 



This may be of two kinds, animal and mechanical. 



By animal power we mean the dii'ect application of the strength of any 

 animal to dragging or pulling, as in the simple case of a horse dragging 

 a cart. By mechanical, the application of any power through the inter- 

 vention of machinery ; the source of power in this latter case may, how- 

 ever, be animal strength, or a purely mechanical agent, as, for instance, 

 a steam-engine. 



The latter is the only species of mechanical power which it has been 

 attempted to apply practically to locomotion ; and therefore that alone we 

 purpose to compare with the animal power. 



Now, although these two powers, viz: simple animal power and the 

 steam-engine, may in most instances be applied so as to produce the same 

 effect, and may, therefore, to a superficial observer appear similar, yet there 

 do exist such essential differences in the mode of action, or the means by 

 which the effect is produced, that there are many cases in which the one 

 may be used, wherein the other may be totally inapplicable. 



In this treatise, draught by animal power is indeed the principal object 

 of consideration ; but as, at the present moment, there appears to be a 

 great effort making to supersede animal power entirely by mechanical — to 

 dismiss our old servant, the horse, and supply his place by the steam- 

 engine — it may be as well, in justice to the former, to say a few words in 

 his defence, and to take a rapid and general view of the distinguishing 

 features of the two agents. 



