STANDARD - Survey Instrument Antique Center!

39
THE WYE LEVEL.
The description of the telescope of the engineer's transit applieg with the following
modifications to the telescope of this level.
It has a clear aperture of 13/% inches focus, and is 17 or 18 inches long over all,
the sun-shade excluded.
The bell-metal collars which rest in the wyes are about 10J^ inches apart and
1^4 inches in diameter.
On account of the extreme length of the telescope tube, four capstan-headed
screws are provided for centering the eye-piece.
The object-glass focussing screw is in the middle of the tube. The eye-piece is
focussed by turning a milled ring at the eye-end. The level attached to the telescope
is about 8 inches long, with about 5K inches exposed, and having a scale graduated
on glass for reading the position of its bubble. The bubble is ground to a true
curvature and barrel form. The sensitiveness of spirit level is graded to the class of
work for which the instrument is intended. The level-tube is suspended from the
telescope-tube in such a manner that at the object-glass end it can be moved in azimuth,
with reference to the telescope axis, and at the eye-piece end it can be moved
in altitude with reference to the same axis.
Its graduated scale is on the level vial tube, and numbered from 6 to to 5 at, each
end of the bubble.
The level-bar is about 12 inches long over all, and at its two extremities supports
the two wyes which rise about 3% inches from its upper surface. One of
these wyes is adjustable in altitude. The level-bar is attached to a long conical
center of the hardest bell-metal, which may be clamped to the leveling plate, and
then a slow motion in azimuth may be given to the telescope, by a slow motion
screw which presses the clamping bar against a stiff spiral spring. With the sunshade
on the telescope, the weight is equaly distributed from the center, each way.
This is necessary, since a sensitive level, in the nicest work, is affected by any
unequal strain, though it may seem to be, practically, imperceptible.
The base, on which the leveling screws rest, has as great a diameter as portability
will permit ; and the leveling screws are cut with a fine thread. These two
points add to the ease with which the instrument may be accurately leveled.
A stop is so arranged that the telescope may be readily set with its horizontal
cross-line level, when the instrument is in adjustment.
The instrument complete is not separable when put into its box. This condition is
necessary to protect one of the essential adjustments of the level the adjustment of
the wyes from needless derangement.