S76 



SCIENCE OF GARDENING. 



Part 11. 



tions. Tliey may be all classed under thi-ee heads, that of transferring a straight line, a 

 curved line, and a level line. ► 



1 926. Where a straight line is to be indicated among objects or inequalities not more 

 than fifteen or twenty feet high, its plan or tract on the earth {jig' 365. a ... 6) may be 

 found by the use of poles, a few feet higher than the elevation of the obstructions, the 

 director being placed on a step-ladder, or other elevation at one end. Where this method 

 cannot be adopted on account of the height of the inequalities, the line must either be 

 foi-med along the summits of these inequalities, which may be done if tliey are houses, 

 hills, or trees ; or parallel lines (c, d, e] formed where practicable, and the main line 

 found by offsets {f, g, h) from those collateral lines at such places as are suitable. A 

 third method, but one not always perfectly accurate, is to take a plan of the field or scene 

 of operations, and on this to set out the proposed line ; then by ascertaining its bearings 

 and distances relatively to the obstructions, it may be transferred from the paper to the 

 ground. In carrying straight lines through woods, lanterns have been used ; but a much 

 more correct method is to elevate poles above the surface of the wood. 



365 



1927. Continuous lines may always be made perfectly straight, however irregular the 

 surface, by following the same parallel as indicated by points of the compass j or by tlie 

 shadow of the operator during sunshine. If the needle does not move, or tlie shadow of 

 the spectator is always projected at the same angle to his course, tlie direction in which 

 he walks, in either case, must be straight. The mode of forming right lines in such cir- 

 cuiAstances being understood, the formation of right-lined figures is merely a repetition 

 of the process, uniting each side by the required angle. 



1 928. Cui-ved lines on irregular surfaces are in general only to be laid down by the 

 previous establishment of straight lines ; first, leading straight h'nes {Jig' 348. a, b, c) and 

 next secondary straight lines {Jig' 348. d, d), which shall form skeletons to the curves. 

 A second mode, and on a large scale by much the most certain, is to find the leading 

 points of th-e curves by triangles from a known base or known bases ; but as both modes 

 are rare in the practice of gardening, they need not be enlarged on. 



1929. Circles, ovals, and every description of curvilinear Jigure may be laid down by 

 either of the above modes ; but ^ here the obstructions are not great, circles, or parts of 

 circles, may be transferred more expeditiously by the following method. The diameter 

 of the circle {Jig. 366.), and any two points {a and c) which 366 



its circumference is to touch, being given, next ascertain the 

 side of the largest square which the circle will contain. Then, 

 if the director place himself in the given point of the cir- 

 cumference, and look eitlier through the sights of a theodo- 

 lite, or along the edge of a common cai-penter's square (rf),- 

 or any right-angled l>oard, the straight line traced by his eye 

 will intersect the situation of tlie circumference of the cir- 

 cle ; if he then causes to be measured along that straight 

 line, the length of the side of the square contained within the 

 circle, the extent of the dimension will deteiTnine a point in 

 the circumference. Then looking along the other side of the 

 square, or through the sights of the theodolite at right angles to tlie former observation, 

 he will by a similar process determine another circumferential point ; and now, by 

 changing his position either to tlie right or left, taking care to set off always the same 

 dimension from tJie side of the square, he will trace out the circumference of the circle 

 or any portion of it. It is evident to any person in the slightest degree acquainted with 



