J 66 Improved Geometrical Plotting Quadrant, &d. 



Secondly. — To determine the Distances of any ttvo inaccessi- 

 ble Objects, both Objects lying in a right Line from the 

 Observer. 



As before directed, place the instrument with its base in 

 the line of the objects; then bv means of the upper limb, 

 set at. 90 degrees, place a staff as a perpendicular at any di- 

 stance at pleasure (say 50, as before). This done, remove 

 the instrument to this second station, and place it so that 

 the upper limb (still at 90°) maybe in the same line as when 

 at the first station : this done, move the upper limb into the 

 direction of the nearest, and the lower limb into the direc- 

 tion of the most distant object; which limbs being so set, 

 and made fast, the distance of both objects from .the second 

 station will be seen on the two limbs, and the distance from 

 the first station at the same time seen on the base line, by 

 setting and moving the perpendicular as directed in the last 

 case. This is also a case of right-angled triangles. 



Thirdly- — To measure an inaccessible Distance in an oblique 

 ./Ingle, where a right Angle cannot be obtained by reason 

 of some Impediment on the Ground. 

 .At the first station, from which the distance is required, 

 place the instrument; then set up a staff, in any attainable 

 direction, to any distance at pleasure (the more distant the 

 better). The instrument being set, with its base in direc- 

 tion to the staff, with one of the moving limbs take the angle 

 of the object, and with the screw fix it thereto. This done, 

 move the instrument in the direction of its base (being be- 

 tween the first station and staff" set up) to any certain di- 

 stance (say 50 yards or measures), as a second station. From 

 this second station again take the angle of the object, and 

 thereto fix the other moving limb ; this done, the distance 

 both from first and second station, as also the bases and 

 perpendiculars thereto, will thus readily be seen. Set the 

 perpendicular at random to any height; move the same till 

 the upper point intersect the upper limb, or that most di- 

 stant from the base ; then read off on the parallel the divi- 

 sions parallel to the base subtended between the two hypo- 

 thenuses or limbs; if this distance or division be equal to 



thfc 



