26 BULLETIN 376, U. S. DEPARTMENT OF AGRICULTURE. 
OFFICE EQUIPMENT AND METHODS. 
Original multiplication, division, and addition were performed on 
mechanical devices. Checking was done by 20-inch slide rules and 
graphic methods. All percentage comparisons were made on 20-inch 
slide rules. Estimate diagrams were checked by proving random 
examples. 
Office procedure. — Where water columns were used at both ends of 
the reach of pipe tested the loss of head in the pipe for the given 
velocity was the difference in elevation between the top of the mean 
water column at gauge No. 1 and the top of the mean column at 
gauge No. 2. Where a mercury manometer was used at one or both 
of the gauges the equivalent water column for each reading of the 
mercury column was computed. The mean of the elevations of the 
tops of the equivalent water columns was accepted as the elevation 
for that gauge. The loss of head was then computed as before. 
Standard methods were employed in computing current meter data 
or weir discharge. Where color was used in timing the velocity of 
the water the time was computed as from the instant of injection to 
the mean between first sight and last appearance of the color at the 
outlet. 
ELEMENTS OF FIELD TESTS TO DETERMINE FRICTION LOSSES AND 
COMPARISON OF OBSERVED VELOCITIES WITH VELOCITIES COM- 
PUTED FROM VARIOUS FORMULAS. 
In the following pages two tables are arranged (Tables 2 and 3). 
Table 2 gives the elements of nearly all known observations on wood 
pipes, either round or square. The various series are arranged in 
ascending sizes of pipe and within one series the observations are 
arranged in ascending order of velocities. 
The tests of one experimenter are omitted from these tables as 
extraordinary friction values were found. The writer made an inde- 
pendent set of tests upon some of the same pipes and found them so 
choked with ravelings from the rock cuts above the siphons that erro- 
neous values were obtained. In the omitted tests the error lay in 
making current meter measurements for Q and then accepting 
Y = -f where A was taken as the nominal area of the pipe when as a 
matter of fact the true value of A was about 90 per cent of the nominal 
A; therefore the true velocity was much higher than that found by 
the erroneous assumption of A. 
EXPLANATORY NOTES ON TABLE 2. 
Column 1 gives the consecutive numbers of the pipes as followed in column 1, Table 
3, also in the discussions in the following pages and in the appendix. The small letter 
a after the numbers refers to discussion in the appendix. Experiments conducted by 
this department are discussed in the text while the essential data secured from other 
sources are abstracted in the appendix. 
