...Railway artillery - Personal Page of GENE SLOVER

650
In the event of lateral displacement of the track, which is inevitable,
the continued use of the same deflection angle and .finite aiming
point does not by any means place the gun on the target. When the
aiming rule is used, the only effect produced by lateral displacement
of the track is the movement of the line of departure of the projectile
te a new path, parallel to the former path and a distance from it
equal to the extent of displacement, which may be only a few inches.
587. In action, the goniometer on the aiming rule is set normal to
the rule. A mirror may be substituted for this goniometer. The
goniometer on the mount is set at the corrected deflection angle.
The mount is moved along the epi by means of the translating
mechanism until the operators at the two goniometers G and 0 are
each able to see the shank of the other goniometer at the same time.
When this is possible, the gun is properly laid.
588. In the rapid determination of both the corrected deflection
and range, Wilson's correction board, plates 472 to 475, is an invaluable
instrument. By its use a computation that may require as
much as an hour with possibility of error m,ay be made with little
mental effort and little chance of error in less than five minutes.
This instrument determines the deflection, corrected for wind, drift,
and parallax. It likewise determines the range corrected for atmosphere,
wind, powder velocity variation, variation in projectile
weight, and height of site.
589. Comments concerning certain of the above factors entering
, into the correction of the range and deflection may be of interest.
With reference to the atmosphere, a certain degree of saturation is
assumed by the French as a standard. The thermometer and barometer
readings then enable one to determine the delUlity. .
590. The air service of the Engineer Corps sends out every few
hours, by wireless, data on the ballistic wind. Their method of determining
the ballistic wind is as follows: Small balloons of a standard
size, about a meter in diameter, are inflated with hydrogen until their
lifting capacity is a certain amount. A balloon is released from a
certain spot which becomes an origin for later computations and the
position of the balloon is observed at regular intervals. From all of
these observed readings mean directions and mean velocities are computed
in terms of various elevations. The information that is sent out
is then: Elevation, X; velocity, Y; direction, Zj Y being the mean
direction of the wind for a maximum ordinate of X. This mean
effective wind for elevation X is called the ballistic wind. This data
is given for various elevations, so that the various battery commanders
firing guns with trajectories of different maximum ordinates will all
have the data they need.
591. The correction board already mentioned may also be used to
analyze certain results in the field. For example, if the range is X,
Digitized by Coogle