768 



Journal of Agriculture. 



[lo Dec, 1910. 



determine a series of points over small areas. The following sketch will 

 serve to show the method of working along a particular line, and having 

 other fixed points it may readily be inferred that any 

 I FTTl I number of interpolations are possible. Take the case of a 



block of land io acres in extent and measuring 10 chains 

 square and having known levels established at its four 

 corners. It is required to ascertain the surface inequali- 

 ties along one of the sides. A and B are pegs ic chains 

 apart whose levels have been ascertained to be 100 ft. and 

 95 ft. respectively. Fix a 3-ft. boning rod at A, B being 

 5 ft. lower ; the boning rod to be fixed there must be 

 made 8 ft. long by temporarily nailing on a piece of 

 quartering. Then the line of sight over the 

 cross-bars of the boning rods, shown dotted above, 

 22. BONING ROD. ^,{\\ ]qq horizontal, and it follows that another rod 

 held at some intermediate point (as at x) and made to coincide with the 

 dotted line will indicate the difference of level. Measure the x rod, sub- 

 tract 3 ft. (height of the rod at A) and the difference is the number of feet 



23. LEVELLING WITH BONING RODS. 



the surface at x is below that at A. Sometimes the rods are rather difficult 

 to see for any distance, but that may be largely got over by wrappnig the 

 head of the rod with a piece of white or coloured paper and sighting 

 towards that one the sun may be shining on. 



There are various devices for taking levels by means of an ordinary 

 carpenter's level fitted with sights ; glass tubes set vertically and con- 

 nected to a horizontal metal tube and partly filled with water, &c., but 

 I do not know of any that are reasonably satisfactory. My advice is to 

 dispense with all makeshifts and face the expense of a surveyor's level. 



{To be continued.) 



.J^ 



