318 Annual Report. 



gress. Now, in the case of the roller, neither the weight of the 

 load, nor of its carriage, rests upon the axle ; and, therefore, the 

 only resistance produced there arises from the weight of the 

 frame, modified as before, by the strain of the moving power; 

 which will, together, produce generally a very small fraction of 

 that resistance which has in this way been obviated. 



Jt has happened that in the patent above alluded to, this cir- 

 cumstance has, apparently, been disregarded; since, for the 

 purpose of preserving the load always in the same position, it 

 has there been proposed to suspend a carriage on an axle inside 

 of the roller, and thus return exactly to the principle of an ordi- 

 nary wr.gon. It is obvious that the two effects of diminishing 

 the resistance as already described, and at the same time pre- 

 venting the load from revolving, are quite incompatible. It will 

 be observed that, in the model of Mr. Naude's contrivance, now 

 in the possession of the Institution, the advantage of the struc- 

 ture would also partly be resigned, if a suggestion shewn in it 

 were adopted ; or if, as .there appears intended, the strain of the 

 moving power were directed to the circumference of the wheel 

 in place of its axis. No advantage could in this way be gained, 

 unless in the hypothetical case, that the diameter of the friction- 

 wheel interposed, could exceed the diameter of the roller itself. 

 From these observations it will be seen, that in those circum- 

 stances where the friction at the axle is almost the only resistance 

 which the moving power has to contend with, (which is the case 

 on a good rail road), by substituting rollers for carriages, the 

 resistance might be reduced to a small fraction of its general 

 amount; so that a horse now able to drag on an average 8 or 9 

 tons, could with the same effort drag above 38*. 



The second part of the resistance, viz : that at the rim of the 

 wheel is, in the case of the roller, nearly all that remains to be 

 overcome by the moving power, and is little affected by the 

 change proposed, if the road or bearing surface be hard and 

 smooth, but where the wheels can sink into a soft material, the 

 advantage is very much in favor of the roller. There is, how- 

 ever, a disadvantage attending the employment of these machines 

 in the great force required to turn them. This Mr. Naude has 

 ingeniously attempted to remedy, by using double rims en- 

 closing friction-wheels ; so that when the roller turns aside from 

 its direction, one end may retire while the other advances. This 

 is an expensive arrangement, but certainly effectual for the 

 intention." 



* To explain this and a preceding allusion, we may remark that the resis- 

 tance of a cylinder of 3 feet in diameter, rolling; on iron, does not appear to 

 exceed I-900dth part of its weight, and that the whole resistance, when the same 

 load is disposed in a carriage with wheels of the same diameter, amounts to 

 ]-200dth. As the resistance arising from the friction at the axis of (he roller is 

 only about ]-200dth of the pressure upon it we attain a ratio nearly 4£: 1, when 

 the axles are of the same size, which would be increased by the comparative 

 smallness of the axle of the roller. 



