s90 A Letter to the Dublin Society 



for the purpose is anii)lv paid for by the increase of bulk that is 

 thus obtained. This I have found to be the case upon the mail- 

 coach road between Edgeworthstown and Longford. Over eight 

 miles of tliis road I have been for some years supervisor, and 

 during that time I have had no reason to complain of the size 

 to which the workmen break the stones with \yhich it is re- 

 paired. 



In the Report of the committee, a machine which I have con- 

 trived for giving an accurate section of a road is alluded to. 



It consists of a rail of deal, twenty-one feet long, three inches 

 wide, and five inches deep. On the top of this rail a frame of 

 wood, eighteen inches long, slides freely: one of the perpendi- 

 cular sides of the rail is covered with paper. 



An arm of wood, eighteen inches long, two inches wide, and 

 an inch thick, is connected with the side of this sliding frame, 

 by means of a common wood screw, upon which this rod tiuiis 

 freely at one end, as upon a centre. Near the other end of the 

 rod a piece of fine black lead or pencil moves horizontally, in a 

 small pencil case, in which it is urged forward by a slender spiral 

 spring. This long rail is to be laid on any road, the section of 

 which is required. The moveable frame, which slides upon the 

 rail as it is moved forward by the hand, permits that end of the 

 moveable rod that carries the pencil, to lie upon the ground ; 

 where, as the frame advances, it rises over every obstacle, and 

 sinks into everv hollow in the road, in the same manner as the 

 wheel of a carriage rises and sinks ; the black-lead at the same 

 time mai.kiug the rise and fall of the rod upon the paj)cr, as the 

 frame advances. 



Besides this contrivance, a similar machine has been employed, 

 for the purpose of delineating the path which that part of a 

 carriage which is upon springs describes ; and at the same time, 

 the path which the axletree which is not upon springs describes. 



A slip of paper several yards long, and five inches broad, was 

 attached to one of the vertical sides of the guide-rail, which is 

 five inches deep, and is in the middle of the platform, A per- 

 pendicular rod was fastened to the axletree of the carriage, so 

 as to rise and fall with the motion of the axletree, as the wheels 

 went over any obstacle, or sunk into any hollow. A black-lead 

 pencil, pressed bv a slender spiral spring, was so placed at the 

 bottom of this rod, as to mark its progress, with all its undula- 

 tions, upon the paper. A similar rod was attached to the body 

 of the carriage, which body was upon springs. This rod was 

 furnished in like manner with a moveable pencil, which de- 

 scribed the path and undulations of that part of the carriage 

 which was on springs ; so that, as the pencils were close to each 



other. 



