LAND SURVEYING. 



569 



ing to a scale fixed on. III. The reducing the measurements 

 of the various triangles, and thence obtaining the total super- 

 ficial content of the whole survey. We shall take each division 

 in order. 



I. The land surveyor requires an assistant in the field, who 

 is called the leader, as it is his business to lead or carry out the 

 chain under the direction of the surveyor, who, for the sake of 

 distinction, is named the follower. The leader is first directed 

 to fix the signals at the angular points of the field ; he then takes 

 the end of the chain in one hand, and the ring of arrows and the 

 cross-staif in the other, and proceeds in the measurement of the 

 longest or base line, under the guidance of the follower, who holds 

 the other end of the chain, and has his field-book ready to note 

 down the various measurements taken. The leader fixes an 

 arrow when he has extended the chain to its full length, and 

 proceeds onward till the follower reaches this arrow, when the 

 chain is again drawn tight, the leader leaving another arrow, and 

 the follower taking up the one first left. The entire line is thus 

 passed over, the leader leaving his arrows as the chain runs out, 

 and the follower gathering them up as the data of the measure- 

 ment. The follower must be careful to observe that the leader 

 keeps in the line between him and the signal towards which they 

 are measuring ; and he must also direct him to give information 

 when he arrives at any point on the line whence a perpendicular 

 may be raised to the angles on either side. When the leader 

 intimates his arrival at any such point, both he and the follower 

 stop, draw the chain tight, and leave it extended on the ground. 

 The follower does not remove the last arrow for the present, but 

 leaves it standing, and lays those he has gathered up beside it ; 

 he then proceeds to the place where the leader has stopped, and 

 taking the cross-staff, ascertains the precise point whence the 

 perpendicular can be raised to the angle. This is done in a very 

 simple manner ; the cross-staff is planted close to the chain, and 

 one of the grooves made to coincide with it ; or, in other words, 

 on looking through the groove in opposite directions, the measurer 

 must see the point whence he set out, and the point to which he 

 is tending ; then looking along one of the grooves at right angles, 

 (without disturbing the position of the cross-staff) he must see 

 whether it bears directly on the angular point; if it do not, the 

 cross-staff must be moved backward or forward along the chain 

 till the precise point is determined ; its position on the line of 

 measurement is then noted in the field-book, an arrow is planted 

 at the spot, and the leader and follower taking their respective 

 places, proceed with the measurement of the remainder of the 

 line; which having completed, the various perpendiculars are 

 measured from the points indicated by the arrows. 



If the subject of the survey be a triangular or quadrilateral 

 field with straight sides, the field work is completed when the 

 longest line,- (that is, the base in the triangle, and the diagonal in 



