FORMATION OF THE FRUIT AND KITCHEN GARDEN. 



13 



marked, all of which shall be in the same hori- 

 zontal line. By measuring down a uniform dis- 

 tance from each of these points, the horizontal 

 line which they marked may be transferred to 

 the ground, or to the height to which the edg- 

 ing is to be worked. If this height be deter- 

 mined at any place, then it is only necessary to 

 measure down to it from the level point origin- 

 ally marked on the rod, and to the same distance 

 below each of the level points the whole edging 

 should be formed. 



If a border were to be made level across a 

 piece of uneven ground, and so that neither 

 more nor less soil shall be employed than that 

 which is found within its limits, the following 

 mode of proceeding may be adopted: — Place a 

 rod at each end, and any number of inter- 

 mediate rods at equal distances. Place the 

 instrument near the middle of the length of 

 the border, but not exactly in the direct line 

 between the rods, in order that these may be 

 seen without obstruction from end to end. 

 Then mark points, in the manner before directed, 

 at the same level on all the rods along the line. 

 Now, as the ground was stated to be uneven, 

 the level points will be at unequal heights above 

 the surface, and the question is, to what uniform 

 distance below them the surface, when levelled, 

 will reach without having soil to wheel away as 

 superfluous, or any to bring in to make up de- 

 ficiencies. We shall suppose the number of rods 

 placed along the line to be ten. Measure down 

 from the level points to the surface of the 

 ground. Then, from these perpendiculars, find 

 the mean depth of the space between the hori- 

 zontal line and the surface of the ground. This 

 is accurately found by the following method: — 

 To half the sum of the first and last perpendi- 

 culars add all the others, and divide the sum by 

 their number, less 1 ; the quotient will be the 

 mean depth of the space between the ground 

 and horizontal line; and a line traced at that 

 depth below the horizontal line will be the 

 ground level to which, if the high parts are 

 taken down, the soil from them will exactly fill 

 the hollows. The following example shows the 

 method of applying this simple rule. Suppose 

 the distances from the ground to the level points 

 marked on the ten rods are as in the accompany- 

 ing table. 



But cases may occur where the ground is so 

 irregular that all the rods in the line cannot be 

 seen from the same spot, and it may be required 

 to find : 



1. The difference of level between the ex- 

 treme points. 



od 1. 



Ft. Ins 

 4 6 







,, 2. 



3 6 



,, 3 



3 



,, 4 



2 6 



„ 5. 



3 



„ 6 



4 6 



., 7 



5 



„ 8 

 „ 9 



„ 10 



2 6 



Sum of first and last divided by 2 3 6 



Sum of the other depths 29 9 



Number of depths, less 1 = 9. 



33 3 

 ) 3 8* 



2. The height of a horizontal line, according 

 to which the ground may be made perfectly 

 level with its own soil. 



3. The direction of a line, according to which 

 the surface will form a uniform slope, with the 

 least possible movement of soil. 



1. To find the difference of level between the 

 two extremities. — Place the rods A, B, c, &c. (fig. 

 797), at convenient distances, and so that the 



surface of the ground will be straight, or nearly 

 so, between every two. The operation may be 

 commenced at either end ; here we shall proceed 

 from A. Place the instrument half-way between 

 A and B, mark the level points on these two 

 rods, and enter their heights from the ground 

 in columns as under. Thus, after directing the 

 instrument back to rod A, the line of sight is 

 found to intersect that rod at 3 feet from the 

 ground ; write that height in the column headed 

 Back-sight. Then turning the sights of the 

 instrument, and viewing forward to rod B, mark 

 the level, and enter its height from the ground, 

 5 feet, in the column headed Fore-sight. Move 

 the instrument to station 2. Take there the 

 back-sight level to B, and the fore-sight one to 

 C, and enter the heights of these level points in 

 the proper columns. Proceed thus till the levels 

 are taken at all the stations : then sum up both 

 columns; their difference is the difference of 

 level. If the sum of the heights in the back- 



