MENSURATION AND SURVEYING 



25 



The height of the tower = TF + AC. 



Or plant any stick vertically and measure its shadow ; at 

 the same time measure the shadow of the object whose height 

 is required. 



Then 



Height of object 

 Its shadow 



Height of stick 

 Its shadow 



Simple methods of levelling. 



A line at right angles to the plumb line is horizontal. 



After driving a few pegs on one level with a bricklayer's 

 level, a peg at a distance on the same level may be driven 

 with the help of boning rods or any three sticks of one 

 height. 



Place two of the sticks over the extreme pegs A and C 

 driven with a mason's level and drive the peg B so that the 

 third stick placed over it is in line with the tops of the other 

 two. Intermediate pegs may similarly be got on the same 

 level. 



The pegs may also be driven on any required gradient. 

 If AB is 3 feet, place upon B a small plank 1 inch thick and 

 level. The gradient from A to B will then be a gradient of 

 1 in 36 and so on. 



