LEVELLING AND LAYING OUT. 



151 



depressions m the ground left, which the corvect basis thus provided furnishes, 

 the necessary data for the exact level which can be maintained by the soil on 

 the spot can be correctly estimated. The trenches themselves can then be 

 •elevated or depressed at pleasure, supposing the right level not to be known 

 when they were formed. When this plan is adopted, the dotted line AB 

 would represent the trench formed, and the dotted vertical lines the levelling- 

 stakes. Grounds with a regular slope in any one direction are managed in a 

 similar manner. Suppose the section that follows is to have a fall of 20 inches 

 in 200 feet, proceed thus : 

 Level the distance ah ; 

 look along the line to c ; 

 make the stake c level 

 with ah ; measure down 

 20 inches to d, and the line 

 ff would form the top of the stakes. Then measure down from the top of each 

 stake^ tlae distance fi-om e to E, and this would give the required level or even 

 surface, EF. However, to make a line of this length, with 20 inches fall, and 

 the levelling-stakes 10 feet apart, a piece of wood, 1 inch thick, must be 

 placed on the top of each stake as you proceed. For instance, the level would 

 rest on the top of the stake at c, but the inch would be inserted under the end 

 at Z> ; it would then rest at h, and the inch be moved on to the next, and so on 

 throughout the entire line. The amount of fall in any given length being 

 given, and the distance between the stakes ascertained, the thickness of the 

 props used will at once be determined. But ground with an even fall is per- 

 haps most expeditiously levelled by the aid of three borrowing-pins, as they 

 ;are termed : they are simply upright splines of wood, say _ 

 2 or 3 inches wide and 1 inch thick, with a cross-piece of the 

 same or greater dimensions, and from 3 to 5 feet long. White 

 is perhaps as good a colour as any, with a black line across the 

 centre of the top bar. Having ascertained the level at any two 

 given points, insert one of the pins, leaving the notch at the 

 bottom resting on the top of the stake. Proceed to the other 

 end, and rest the pin on another stake, even with your intended 

 surface ; send a boy or man along the line to insert stakes at 

 convenient distances, say 15 or 20 feet apart, and place the 

 third borrowing-pin on them as he proceeds. When the eye sees the three 

 pins— which, of course, are all of a length— at once, then the stake is right, 

 and he immediately proceeds 

 to insert and prove, and thus 



u 



goe-5 on through out the whole _^ 



line. If the distance is too^^ 



great to see the entire length, 



the observator, instead of continuing at one end, can follow within a few stakes 



of the operator, or the stationary pin can be inserted in the middle instead of 



at the end. This sketch will illustrate my meaning. 



