104< WHEEL CARRIAGES. 



great many more points than a narrow one, the 

 friction must, of course, be just so much the 

 greater, and consequently there must be so many 

 more horses to draw the waggon. But they did 

 not consider, that, if the whole weight of the wag- 

 gon and the load in it bear upon a great many 

 points, each sustains a proportionally less degree 

 of weight and friction, than when it bears only 

 upon a few points ; so that what is wanting in 

 one, is made up in the other ; and, therefore, the 

 friction will be just equal under equal degrees of 

 weight, as may be shown by the following easy 

 experiment : 



Let one end of a piece of packthread be fastened 

 to a brick, and the other end to a common scale 

 for holding weights ; then put the brick edgeways 

 on the table, and let the scale hang over the side ; 

 put as much weight into the scale as will just draw 

 the brick along the table. Then taking back the 

 brick to its former place, lay itjlat, and leave it to 

 be acted on by the weight in the scale as before, 

 and it will draw it along with the same ease as when 

 it lay upon its edge. Jn the former case, the brick 

 may be considered as a narrow wheel on the 

 ground, and in the latter as a broad wheel. And 

 since the brick is drawn along with equal ease, 

 whether its broad side or narrow edge touch the 

 table, it shows that a broad wheel might be drawn 

 along the ground with the same ease as a narrow 

 one (supposing them equally heavy,) even though 

 they should drag, and not roll, as they go along. 



As narrow wheels are always sinking into the 

 roads, they must be considered as constantly going 

 up-hill, even on level ground; and their sides must 

 sustain a great deal of friction by rubbing against 

 the ruts. But both these inconveniences are 



