766 



Journal of Agriculture. 



[lo Dec, 1910. 



The " Remarks " column indicates tlie places at which the staff was 

 held. There was no necessity to write in " Point i, 2, &c., as the 

 " distance " column already shows the measurements in chains, but it was 

 added in the endeavour to make everything clear. The first of a series of 

 readings is always called a " Back sight" and the last a " Fore sight," 

 all others being " Intermediate " no matter where taken. The R.L.'s 

 are found by adding or subtracting the rises or falls deduced from suc- 

 cessive sights. If it becomes necessary to turn over a leaf of the level 

 book, enter the last sight taken before doing so as a " Fore " sight and on 

 turning over enter it again at the top of the page as a " Back " sight and 

 proceed with the series of readings as before. To prove that your work 

 is correct as shown in level book, add up the columns marked " Back sight, 

 Fore sight, Ri.se, and Fall." The differences between the first two and 

 the second tw^o should be equal and equal also to the difference between 

 the first and last R.L., as shown in the specimen of level book. This 

 should be done on everv page. It is well to rememlier that when a Fotp 

 sight is greater that a Back sight it indicates Fall, and vice ver'^d. With 

 the aid of the drawings and specimen pages given, and with a little 

 practice, it is hoped that the operation of taking a series of levels over 



B.M.ontree.N^-Z 



20. SETTING OUT A CONTOUR CHANNEL. 



any piece of country has been so explained and simplified as to remove 

 many imaginary difficulties and to encourage land-holders to attempt it for 

 themselves. 



Further on will be found a drawing showing level contours, and 

 later, level head ditches are referred to. Such contour or level lines 

 may be projected over country independent of any system of chessboard 

 levelling. Starting from some point selected for its convenience for dis- 

 tributing a supply of water, set the instrument up distant therefrom 

 about 4 or 5 chains and as nearly on the same level as the eye can esti- 

 mate. Read the staff at the initial point and cause the staffman to pace 

 along the estimated line, one or two chains, or more or less according to the 

 accuracy of location desired. Cause him then to move the staff up or down 

 the slope of the land and as nearly as may be at right angles to the esti- 

 mated course, until the staff reading shall coincide with that first taken. 

 Fix a stake there (stakes 24 ins. or 30 ins. long are convenient) and repeat 

 until he shall have reached 8 or 10 chains, i.e., 4 or 5 chains beyond the 

 instrument. At that point cnuse him, in addition to a stake, to fix a 

 short peg flush with or slightly above the surface of the ground, the top 

 of which shall give the same staff reading. Repeat the process as far .1 = 



