210 



MASSACHUSETTS AGRICULTURE. 



long, having a grade of only 1^ or 2 in a hundred, in the line 

 of the road at proper intervals. An expedient adopted by 

 Telford, the eminent English engineer, in order to avoid making 

 a piece of road a mile long, on a less grade than 5 in a hundred, 

 on account of the increased cost this would have occasioned, 

 and yet not have this part of the road too much more tiresome 

 for the horses than the rest, was to make the road-surface on 

 this mile of a much better quality than on the remainder ; the 

 additional cost required for the improved road-bed amounting 

 to only about one-half of what it would have cost to reduce the 

 grade to say 4 in a hundred, as will be again referred to under 

 the head of trackways. In sharp curves the grade should be 

 only 1 or 2 in a hundred or level. 



The following table gives the effects of various grades on the 

 amount a horse can pull, and is based on calling the load a horse 

 will pull on a level, one : — 



To determine whether it is most advisable to go over or around 

 a hill, all other considerations being equal, we have this rule : 

 Call the difference between the distance around on a level and 

 that over the hill, d, the distance around being taken as the 

 greatest, and call A, the height of the hill. 



Then in case of a first class road, we go around when d is less 

 than 16 h. 



And in case of a second class road, we go around when d is 

 less than 10 h. 



When the height of a necessary embankment gets to be more 

 than 60 or 65 feet, a bridge or viaduct will be found cheaper, and 

 the same measure, 60 feet, applies in case of tunnels, they being 

 cheaper at that depth than open cuttings. 



