Observations upon Wheel- Carriage Experiment s. 255 



percli has several advantages, and a short perch many serious 

 disadvantages, from causes which have not yet come before the 

 public, either by experiment or in print ; one cause will how- 

 ever be considered, when observing u])on experiment No. 6 in 

 syllabus. It will there appear, I presume, that similar disad- 

 vantages with respect to draught may l5e produced by shortening 

 the perch, or by the elevation of the centre of gravity. 



Experiment No. 6, see annexed syllabus. 



The question of advantage or disadvantage, by the difference 

 of height of the centre of gravity of a loaded carriage, involves 

 the necessity of considering the effect of the increased velocity 

 and distance of its motion upon a laterally inclined road, a road 

 of many ruts, or of short ascents or descents: this motion I would 

 presume to be seriously diadvantageous, and it is increased pro- 

 portionately with the height of it. The experiment, as I un- 

 derstood, was supposed to show that variation with respect to 

 height made no difference as to facility of draught or otherwise. 

 The surface used in this case was a tolerably smooth pavement ; 

 had it been a very bad road, with various lateral inclinations, I 

 am inclined to think, for the reasons following, that the eleva- 

 tion of the weight to the height, which is very common practi- 

 callv, would have appeared to be seriously injurious. 



By the first effect of a sudden lateral inclination all the wheels 

 at the same moment have a force acting upon them in a direc- 

 tion nearly at a right angle with the direction of the forces ap- 

 plied by tlie horses ; a worse effect may be produced bv ruts al- 

 ternately at either side, the velocity of the centre of gra^itv, and 

 the distance passed through by it, must in these lateral motions 

 increase in proportion to its height, and thereby it will swing 

 with additional violence from side to side. Again, when the 

 front wheels of a carriage fall together into a hollow or rut, the 

 weight upon that axle becomes increased proportionally to the 

 diminution of the length of the perch, and the height of the 

 centre of gravity; in this case of the short perch, the angle 

 formed by it with a horizontal line will be nearly double in a rut 

 of a given depth what it would be, if the perch were of double 

 the length. The same increase of weight acts upon the hinder 

 axle when in the rut or hollow; som.e proportion of these disad- 

 vantages may be countervailed by the axle, that is out of the rut, 

 having less weight upon it than in ordinary; notwithstanding 

 which, I have no hesitation in thinking that it would be judi- 

 cious, l)y lowering the centre of gravity or by lengthening the 

 perch, to avoid increasing the weight upon the axle in the rut, 

 because in the one case tiie weight is to be lifted upwards, and 

 in the other to be drawn horizontally. The general impression 

 of increased power, by shortening the distance between the horse 



and 



