ook, in front of the camp. It had been
a great nuisance to keep our filter barrel full. Every few days we would
have to form a bucket brigade, passing pails of water up the line until
the barrel was filled. Now Bill proposed to do away with all this bother
and let the river do the work for us.

SURVEYING FOR THE WATER WHEEL.

We first determined the height of the upper filter barrel above the
level of the river. This was done with our surveying instrument, which
was set level with the top of the barrel. We sighted with the instrument
to a long pole that was held upright at the edge of the water. The pole
had been marked off into feet with white chalk marks, and on sighting
through the sight holes we found that the hairs came in line with the
eleventh chalk mark. The top of the filter was, therefore, 11 feet above
the level of the river. Bill figured that it would be necessary to
construct a wheel about 15 feet in diameter in order to raise the water
to the proper height.

[Illustration: Fig. 250. Surveying for the Water Wheel.]

TOWERS FOR THE WATER WHEEL.

[Illustration: Fig. 251. Frame for Large Tower.]

First we built the towers to support the wheel. One tower was 16 feet
high and the other only 10 feet. The large tower was made something like
a very tall and narrow saw-horse. Two stout poles 17 feet long were
flattened at their upper ends and nailed together, with the ends
projecting about a foot, as shown in Fig. 251. At the bottom these poles
were spaced 8 feet apart by a cross bar, and about 9-1/2 feet from the
bottom a pair of boards were nailed to opposite sides of the pole to
serve as supports for the axle of the water wheel. Another pair of
17-foot poles was now similarly fastened together and then the two pairs
were spaced about 12 feet apart and connected at the top and bottom with
boards.

[Illustration: Fig. 252. The Large Tower.]

[Illustration: Fig. 253. V-shaped Trough.]

At the top two smooth boards were used and these were nailed to the
inner sides of the projecting ends, which were tapered off. In this
manner a V-shaped trough was formed. The boards were firmly nailed
together at their meeting edges so as to prevent them from warping
apart. A diagonal brace at each corner made the wedge-shaped tower very
substantial. A number of cleats nailed to one of the poles provided a
ladder by which we could mount to the top of the tower. The shorter
tower was a three-legged affair, made of thre