WHEEL CARRIAGES. 125 



latter case, three of the horses must draw horizontaiiy, and there* 

 fore in a manner inconsistent with their mechanism. 



Truth of this proved by practice — The small horses of the north 

 of England draw larger weights than the largest waggon-horses of 

 London, and go longer stages. The small horses of Ireland will 

 draw as a common load 15 cwt., while our best waggon horses do 

 not draw, on an average, more than 10 or 12 cwt. 



In the rase of our eight-horse waggons, at least, six out of the 

 eight horses draw inconsistently with their mechanism, so that 

 much exertion is misaj)p!ied ; the horse's collar is als^) drawn 

 against his throat, and his breathing interrupted. 



in cart teatijs, where the horses are not marshalled, as in wag- 

 gons, one horse is standing still while another is wasting his strength 

 in pulling him forward. One liorse leans one way out of the line 

 of draught, whilst another is leaning a contrary way ; their strength, 

 in short, is scarcely ever united. 



A horse, moreover, hasthe momentum of his draught increased 

 by having a portion of the weight on his back. Hence, low wheels 

 are not so disadvantageous as is generally supposed ; for low wheels 

 oblige the line draught to incline agreeably to the natural draught 

 of the horse. 



To prove that a horse should have something to lift in his 

 draught, to give that draught its utmost momentum, Mr. W. men- 

 tioned that he had made the following experiments : — 



He constructed a model of a four-wheeled carriage, whose weight 

 was 82 ounces, the fore wheels 8 1-4 inches, and the hind wheels 

 10 1-2 inches. This was drawn on a horizontal board by a line 

 over a pulley ; an obstacle 1 1-2 inehes high was placed before the 

 fore-wheels, and the splinter-bar raised on the futchels, so as to be 

 even with the top of the foic-whecl. The line of draught was 

 then horizontal. 



When things were so disposed, the weight necessary to draw the 

 fore-wheels over the obstacle was 42 oz. 



On lowering the splinter-bar, so as to make the line of draught 

 to be from three-fourths the height or diameter of the wheel, the 

 weight required was only 30 oz. 



By lowering t!ie splinter-bar still farther, so as to make the line 

 of draught from the uxlc, tlie weight required was reduced to 24 

 ounces. 



On changing the point of draught to a splinter-bar one inch be- 

 low the axle of the fore-wheel, the weight was only 22 1-2 ounces. 



It was hence to be seen, that the disadvantages of drawing from 

 above the centre are as the sines of the respective arcs passing 

 through the splinter-bar; and the advantage of drawing from be- 

 low the centre, also as the sines of the respective arcs. 



Now, as the splinter-bar, or point of draught, in most of our car- 

 riages, is placed about one-fourth the diameter of the forc-whee! 

 above its centre, it is evident that a fortuitous pressure, equal to 

 one-fifth of whatever weight lies upon it, is actually added to t!,o 

 natural weight by this unn?Uiiral situation of the point of draught 



