TRANSPORTATION ON LAND BY VEHICLES; -THE ROADS 



37 



I. Instruments for measuring vertical angles. Instruments reading per cent are preferable to those reading 

 degrees. The horizon is established by a plumb bob or by a spirit level. 



(a) Plumb bob instruments. 



1. The"Bose." The instrument itself is a plumb bob. It consists of a metal frame hanging from 

 a horizontal pin on a Jessup staff 5 feet high. The target or flag has the same height. The 

 base of the metal frame is weighted down with lead. The vernier with ocular hole slides up 

 and down on one side of the me- 



tal frame, which is subdivided into 

 percentages of grade. The object- 

 ive thread is stationary in the midst 

 of the other side of the metal frame. 

 The distance between the ocular 

 hole and the objective thread is 

 100 units when the vernier is pla- 

 ced at zero. The Bose, costing 

 :y20, in the hands of a forester 

 understanding the instrument,works 

 with an accuracy of decimals of per 

 cents. Mistakes are readily discov- 

 ered and readily repaired in the 

 woods. Mistakes are possible if:- 

 Either target or staff is held 



obliquely; 

 The staff is not inserted into 



the same hole and to the 



same depth into the hole 



which was used by the 



target; 

 The target is not e.xactly as 



high as the objective of the 



instrument; 

 The plumb bob fails to place 



the zero-line of the instru- 

 ment horizontally. 

 The correctness of the instrument 

 can be controlled readily when 

 target and instrument are made to 

 change positions. 



2. The "Brandts clinometer" consists 

 of a small metal case in which is 

 suspended, on a delicate a.xle, a 



small wheel, with the circumference graded in degrees. 

 is attached to the wheel case 



/TTs 



Bose road level and target thereto. 



An open telescope, without lenses, 

 The wheel is held in perpendicular position by a lead weight 

 at its base. Sighting through the telescope, the gradation on the circumference of the wheel 

 is read simultaneously. 



A number of forest instruments usuaWy used to measure the height of trees ("hypsometers") can 

 also be used to determine the grade of roads. The Weise, the Klausner, the Koenig, the 

 Faustmann, and the Pressler can be thus used to good advantage. When the distance scale 

 of these instruments is placed at 100, the grade of the roads is read directly in per cent. 



