10 
BULLETIN 194, U. S. DEPARTMENT OF AGRICULTURE. 
mining the exact surface of the water at the ends of the reach in 
order to measure the fall as was the following arrangement. 
Bench marks. — In his experiments in Utah, S. Fortier determined 
the hydraulic slope of the water surface by leveling between the tops 
of nails, sharpened at both ends and driven into stakes whose tops 
were below the surface of the water. 1 After considerable experimen- 
tation the writer decided that this general arrangement was better 
than that involving a line of levels between the ends of the reach 
and in addition another chance of error in measuring down from the 
established bench marks to the surface of 
the water. However, the writer modified 
Dr. Fortier's plan in the following manner: 
It was found that driving the nail, sharp- 
ened at the top as well as at the bottom, 
dulled the point at the top so that it did 
not make a good point in order to get a 
"bead" on the surface of the water in a 
stilling box, and it also did not make a 
solid bench mark from which to run levels. 
A better bench mark would be the ordinary 
top of a well-made wire nail, but this is 
not directly adaptable, as it can not be 
driven to a nicety as a surface gauge. To 
obviate this feature the device shown in fig- 
ure 1 was constructed. It consists of a 
motor-cycle spoke soldered into a hole near 
the edge of the surface exposed by cutting off 
a three-eighths inch punch. The spoke was 
bent in the form of a buttonhook and care- 
fully sharpened. The end of the spoke 
forming the pointed hook was originally 
threaded for the nipple, which was retained 
and served as a protection to the point 
in carrying the device. The final sharp 
point is in the same plane as the clean 
Therefore, if the wire nail is driven by 
means of the punch, in much the same manner as a carpen- 
ter sets a nail below the surface of wood with a carpenter's punch, 
then the top of the wire nail is just flush with the surface of the 
water when the sharp point of the hook shows at the surface of 
the water as an ordinary hook gauge. This presupposes that the 
punch has been held truly vertical in setting the nail. This was 
assured in the following manner: Near the top of the punch two 
holes one-sixteenth inch in diameter were bored at right angles to 
Fig. 1.— Hook device for setting 
nail head flush with water sur- 
face, two-thirds size. 
cut end of the punch. 
i U. S. Geol. Survey, Water-Supply and Irrig. Paper 43 (1901). 
