Garden Surveying, Levelling, and Mensuration 217 



the right or left of the chain line. Thus, in the specimen page of the field 

 book given here (fig. 401), it will be noticed that at 20 links there is an 

 iron fence 26 links to the right of the chain line, and this iron fence gets 

 as near as 12 links when the straight line has been chained 200 links. 

 In the same way, on the left, the " farm road " is indicated as 8 links to 

 the left, while the corners of a building are shown to be at various distances 

 from the chain line. Although there is a column in the field book it must 

 be regarded as a single line, and not as two distinct ones. Thus, when the 

 farm road crosses from left to right at 228 and 246 links, the lines indicat- 

 ing it appear opposite the point at which they intersected the chain line. 

 In surveying a piece of land, chain lines should be marked out so as to take 

 in the most important features or to form the longest and best base lines. 

 Afterwards the chain lines with their stations and distinctive features can 

 be plotted to scale on paper, and will give a correct idea as to the shape 

 of the land surveyed. The area is then computed by measuring up the 

 triangles or rectangles made by the various chain lines. 



Offsets. The distances to the right or left of a chain line are marked 

 off by means of "offset" staffs, each 10 links (79'2 in.) long. Each link 

 is painted alternately red and white, or black, and numbered; and the 

 bottom end is pointed to stick in the ground. Offset distances are always 

 taken at right angles to the chain line; but those for buildings are taken 

 obliquely for the corners, as shown in the sketch. 



LEVELLING 



In laying out a garden, or in re- 

 ducing a piece of undulating ground 

 to the level of a bowling green, 

 cricket pitch, or tennis ground, the 

 art of levelling is a useful accom- 

 plishment. A simple method of 

 taking levels, and one usually suf- 

 ficient for most horticultural and 

 agricultural purposes, is by means 

 of " borning " or " boning :> rods and 

 spirit levels. Three boning rods are 

 used, each consisting of a straight 

 piece of smooth batten about 4 ft. 

 long, with a shorter crosspiece on 

 top, the whole resembling the letter 

 T. Sometimes the boning rods are 

 all alike, but there are variations. 

 The crosspiece in some cases is an 

 inch wider than in others, and a small sighting hole is pierced in it just 

 1 in. from the upper edge. On looking through this hole, and sighting 

 over the second and third rod (each of which is held by an assistant) it 



Fig. 402. Boning Rods 



