TILE DRAINAGE. 98 



the proposed ditch, at each hundred -foot engineer's stake, 

 and tack a lath or batten exactly le>vel across the ditch to the 

 top of these stakes, so that the top of each lath, or sight ing- rod, 

 shall be exactly 66 inches (5| feet), for example, above where 

 the bottom of the ditch must be at that point, as shown by 

 the engineer's figures. Then have a u sighting-stick," or 

 batten witli cross-stick at hand, itself also just 66 inches long 

 (a convenient length for sighting over for the average man), 

 and, as you dig your bottom course, occasionally set the. 

 sighting-stick as nearly plumb as you can (this is important) in 

 the bottom of the ditch as there dug, and hold it plumb with 

 one hand, and sight over it, thus held, to the next two or 

 three sighting-rods down or up the ditch. If the top of your 

 sighting-stick is in exact line with the sighting-rods, your 

 ditch at tha^ point is at the right depth. If it is not so, then 

 make it so. Or, you may use your body as a sighting-stick, 



"sigh ting stick" to 



Fig. 25. Position of workman sighting 1 over the "sightL.e, , 



the " sighting-rods." Here he stands in the ditch (one side represented 

 as removed at that point), and sights along- the ditch already dug. 



setting your sighting-rods the exact height of your eye as you 

 stand erect, and simply standing erect in the bottom of the 

 ditch each time you sight for grade. Fig. 25 gives the sight- 



