42 Implements. 



the level at B and the levelling rod at A we take the read- 

 ings of that point : 8 feet. Stake 1, when driven in to a 

 sufficient depth, should be 1 foot 3 tenths lower; the read- 

 ings at that point will therefore l>e : 1' 7" + 8' = 9' 7". 

 Stake 2. 18 feet distant, is 7 tenths higher; the readings 

 will l>e 9 feet, and so on in proportion. 



The levelling rod is simply a square stake, about ten feet 

 high, divided into feet, each foot being subdivided into 

 tenths and hundreds. The main divisions are painted red 

 and white alternately. While the levelling is being done, 

 the rodman is directed to hold a lead pencil in a horizontal 

 position across the rod, moving it up and down slowly 

 until the exact place is found. A more complete levelling 

 rod is provided Avith a round target which slides up and 

 down. The surface of the target is divided into four equal 

 sections painted alternately white and red; there is an 

 opening in the centre to admit of reading the number of 

 feet and inches indicated. 



The Y-level is quite an expensive instrument used for the 

 same purpose, and in the same manner as the water-level, 

 being of course more exact and more useful for important 

 work. It consists of a telescope with a tube of brass or 

 gun-metal, and lenses provided with a hair-cross of spider's 

 webs, allowing very accurate observations. It is levelled 

 with the aid of two air-bubbles in glass tubes, and by means 

 of screws acting upon a pivot, placed loosely in the socket. 

 A tripod is always used in connection with this instrument. 

 It requires a very careful adjustment and cannot be used in 

 a satisfactory manner without some practice. The theodo- 

 lite combines the qualities of the compass and the Y-level. 



