246 MASSACHUSETTS AGRICULTURE. 



crease in velocity ; this increment is however less, the softer 

 the track or road and according as the vehicle is best provided 

 with springs. 



5. On soft earth embankments, or on sand or sods, or on 

 streets newly covered with gravel, the tractive force is indepen- 

 dent of the velocity. 



6. On a well made pavement of regular shaped stone, the 

 tractive force, horses on a walk, is about three-fourths of that 

 on a good macadam road, but with horses on a trot, the two are 

 about equal. 



7. The wear on the road is greater the smaller the diameter 

 of the wheels and greater in the case of vehicles without, than 

 for those with springs. Most road-rollers, as now in use, have 

 too small a diameter besides being too light and consequently 

 do not properly compress the road surface. 



8v The tractive force, as well as the wear on the road, is 

 greater in the case of vehicles that have their wheels placed at 

 an angle with the vertical by reason of the ends of the axle-trees 

 being bent down, than for those that have their wheels set plumb 

 and the centre line of the axle-trees level. 



