2-60. Wooden Towers. When it becomes necessary to raise the line of sight to clear obstructions on
longer lines, a stable tower must be built. It is necessary to construct an instrument stand and a separate
platform to support the observer. The whole structure is referred to as a tower. Wooden towers are built
at the station, using lumber or natural forest materials.
a. Towers should range between 6 and 25 feet high. It is not considered practical to build wooden
towers higher than 25 feet. When greater heights are needed, aluminum or steel towers are used. The
materials normally on hand and the easiest to handle are 2-inch x 4-inch x 16-foot, 1-inch x 4-inch x 16-
foot, and 1-inch x 12-inch x 16-foot boards. For towers over 15 feet, 2-inch x 4-inch boards are usually
doubled on the lower two-thirds or so of the tower's legs. The inner or instrument tower is built as a
tripod, usually completed on the ground and set up in leg holes as one piece. The scaffold supporting
the observer's platform is usually four legged, with two opposite sides put together on the ground and
stood up around the tripod. All legs are laid out and marked on the ground. One side each of the tripod
and the scaffold is used as a pattern to cut the horizontal ties and diagonals the same for all sides. The
instrument tripod is not guyed during observation, but it may be weighted with rocks or other weights to
increase its stability. In higher order work, no observations should be made on higher wooden towers
during extremely high winds. However, the instrument tripod may be guyed when not in use to prevent
damage from high winds.
b. The outer tower must be strong enough to be safe and must not touch the inner tower at any
point. It should be provided with hand railings, as an observer often loses his sense of balance
momentarily when taking his eyes away from the telescope. If necessary, the outer tower should be
guy-wired at all four corners.