62 BULLETIN 376, U. S. DEPARTMENT OF AGRICULTURE. 
Throughout approximately the last 100 feet of wood pipe ending at 
a, Plate IX, tapering staves are inserted in the pipe until an elliptical 
section 12 feet wide and 9 feet high is reached at a. The area has been 
increased so gradually up to 84.82 square feet that, it is computed, 
3.99 feet of velocity head have been recovered, the velocity meanwhile 
being reduced to 1 1 .8 feet per second. Between b and c the transition 
section changes from an elliptical to a rectangular shape 13f feet wide 
by 10.6 feet high, with an area of 153.12 square feet. In this transi- 
tion section the vertical walls and flat floor and roof begin at b with 
zero width, increasing to full width at c, the corners being rounded 
out in the concrete. The velocity is further diminished to 6.54 feet 
per second and the computations show an additional velocity head 
of 1.51 feet recovered. At the upper end of the canal leading from 
the structure the velocity is further reduced to 2.10 feet per second by 
enlarging the section, the additional recovered velocity head being 
computed as 0.59 feet. Thus of the 6.14 feet devoted at the inlet end 
to increasing the velocity, the computations show the recovery of all 
but the 0.05 foot, which is due to the difference in velocities in the 
channels above and below the structure. However, even with care- 
fully designed transition sections the computations show an aggregate 
of 1.80 feet devoted to "entry head" at the various changes in cross 
section. 
The outlet structure of the Similkameen Siphon of the West Okano- 
gan Irrigation District, Washington, is also designed with a view to 
conservation of velocity head. This structure (B, PL IX) consists 
of a 46-inch stave pipe tapered in a length of 12 feet to a diameter of 
57.5 inches, the pipe then discharging into a wooden flume. The 
most noticeable feature of the structure is the use of guide wings 
extending into the flume. These prevent a sudden enlargement of 
the cross section at the end of the pipe and tend to recover the veloc- 
ity head. The floor of the flume is extended into the pipe to the point 
where the taper section begins, thus preventing contraction and con- 
sequent loss of head due to extension of the segment of the pipe below 
the floor line at the bulkhead. No attempt is made to secure water- 
tightness in these guide wings, but the water is allowed to enter 
between the wings and the flume proper so that no pressure may be 
brought against the light wings. All tightness is secured at the bulk- 
head and in the flume proper. 
Where a change is made in the size of pipe a long taper transition 
section is usually installed. In the Altmar pipe (No. 51) the diameter 
is changed from 12 to 11 feet. This change is so gradual that it can 
hardly be detected by the eye. In a similar way the Mabton pressure 
pipe (Nos. 43, 45, and 46) is reduced from 55 J inches to 48J inches. 
Where changes in sectional area are made in this manner probably 
