ON DRAUGHT. 519 



experiment on a large scale, that he found they materially assisted in keeping the 

 roads in repair, and diminished the draught in the proportion of five to four. 



Amidst such conflicting and contradictory opinions, it would appear difficult 

 to come to any useful conclusion, and we might naturally be disposed to 

 adopt a very common practice, that of taking an average result. 



A little consideration, however, will show that these apparent discrepancies 

 and contradictions arise, in great measure, from attempting to generalise and 

 apply to practice the results of experiments made in, and therefore applicable 

 only to, particular cases. 



The results of experiments thus made at various times and places, and 

 without that identity of condition and circumstance so necessary when standard 

 rules are to be deduced from them, have, nevertheless been used for that purpose ; 

 and this circumstance, combined with the variety of distinct points to be consi- 

 dered before we can estimate accurately what even constitutes draught, will per- 

 haps account for the disagreement among the practical and scientific authorities 

 alluded to. 



We must therefore examine severally all these points ; and then, by con- 

 sidering their relative bearing upon each other, we may hope to reconcile the 

 different opinions advanced, without which we cannot collect from them any 

 information which will lead us to a practical and beneficial result. 



We shall proceed to divide the subject under separate and distinct heads, 

 and under each head to examine the methods or means now in use, or which 

 have been proposed, and endeavour to estimate their comparative advantages by 

 availing ourselves of what is already written and known upon each. 



It will be necessary first, however, to explain and define clearly some terms 

 which will occur frequently in the course of this paper, and especially the word 

 ' draught,' which is itself the title of the treatise. 



This word is used in such a very general and vague sense, that it would be 

 difficult, if not impossible, to give an explanation which should apply equally 

 to all its different meanings. 



In the expression ' draught by animal power,' it would seem to mean the 

 action itself of drawing ; while, on the other hand, it is frequently used to signify 

 the amount of power employed, as well as the degree of resistance as when we 

 say the draught of a horse, or the draught of a carriage. l Draught power' is 

 also an expression used. We shall, however, confine our use of the word to 

 the two meanings draught, the action of dragging and draught, the amount 

 of resistance to the power employed to drag any given weight. 



' Force of traction,' is another expression requiring explanation ; but here 

 we must enter into more detail, and give a practical illustration of our meaning. 



A force is most conveniently measured by the weight which it would be 

 capable of raising ; but it is not therefore necessarily applied vertically, in 

 which direction weight or gravity acts. 



If a weight of lOOlbs. be suspended to a rope, it is clearly exerting upon 

 this rope a force of lOOlbs. ; but if the rope be passed over a pully void of 

 friction, and continued horizontally, or in any other direction, and then attached 

 to some fixed point, the weight still acts upon all parts of this rope, and con- 

 sequently upon the point to which it is fixed, with a force equal to lOOlbs. : and 

 BO inversely, if a horse be pulling at a rope with a force which, if the rope were 

 passed over a pully, would raise lOOlbs., the force of traction of the horse is 

 in this case lOOlbs. Spring steel-yards being now commonly in use, we 

 may be permitted to refer to them as affording another clear exemplification of 

 our meaning. In pulling at a steel-yard of this description, if the same force 

 be exerted, whether horizontally or vertically, the index will, of course, show 

 the same amount ; and, consequently, if the strength of the horse be measured 



