lo Dec, 1910.] Irrigation. 765 



weather. Such a staff will be found both durable and satisfactory. 

 Face graduations printed on paper may be purchased from an instrument 

 maker, but are apt to become distorted when being pasted on. 



The best staff is of course that commonly used by surveyors and others, 

 and the most convenient length is 14 feet. It is made on the telescopic 

 principle and when closed is about 5 feet long. Second-hand staves such 

 as these may be bought for about 15s. 



Although it appears a simple matter to hold a staff for instrumental 

 observation, care is necessary to insure reliable results, and particularly 

 when the survey is of some extent. The staffman must stand behind the 

 staff and face the level, holding the staff at about breast height with 

 both hands, and keeping the fingers clear of the graduated face. The 

 staff must rest on a firm footing and be held truly vertical, and at all 

 terminal readings, usually the last reading before the level is moved, a 

 small peg should be driven leaving its head slightly above the surface 

 before that reading is made, or some solid object should be chosen, so 

 that when the staft' is again read at the same point from another position, 

 there shall have been no movement. With a telescopic staff make sure 

 that the catch holding the leaves in position is acting. It is net otten 

 that more than 6 or 8 feet of a staff is used. A little practice will 

 insure a habit of holding it correctly, but if considerable accuracy is 

 desired, the staffman should be provided with a plumbob to check ver- 

 ticality, and in soft ground should see that no mud adheres to the foot 

 of the staff. Ho\ve\er, as a rule, a farmer does not require a great 

 deal of nicety when attempting grading work, and some of these pointers 

 may be neglected. 



By reference to the plan (No. 12) it will be observed that every peg has. 

 a particular designation and is easily referred to. Thus, all lines running 

 E. and W. are numbered i, 2, 3, &c., and those running N. and S. are 

 numbered a, b, c, &c., and the pegs at the intersections are conveniently 

 known as la, ib, ic, or 2a, 2b, 2c, as the case may be. 



Level Book. — ^To make this clear a specimen page of level book is 

 appended and indicates how the observations are entered and converted 

 hito ■■ Reduced levels,"' such as are shown on the plan. Books already 

 ruled may be purchased cheaply at any leading stationers. When order- 

 ing, send copy of the form here used, as there are others which might 

 easily lead to confusion.. By the term " Reduced levels" is meant that 

 all levels are reduced to some common point of origin, rendering compari- 

 son of points at any part of the survey merely a matter of inspection. 

 Thus the " R.L." at peg oa is 100.00 feet, while that at 7h is 100.97 show- 

 ing that the last point is the higher by 0.97 feet, practically i foot. 



Surveyors and engineers take for the origin of their levels the mean 

 level of the .sea. hence in all subsequent operations their height above .sea- 

 level is apparent. But. to the man on the land, this is usually a matter 

 of indifference and any convenient height may be assumed, as in the pre- 

 sent case at oa where 100.00 feet has been adopted. It is merely a means 

 of making successive levels comparable, and may be any number or height 

 the observer chooses, but it is important that, once chosen, it should be 

 followed up, or confusion and much annoyance may arise. Frequently, 

 when giving addresses on the subject of levelling, I have had the greatest 

 trouble in making it clear that the staff readings are merely a means to- 

 a-i end — the determination of "Reduced levels." And also, to make it 



