...Railway artillery - Personal Page of GENE SLOVER

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the corrected range Y, and the center of impact of the group of shots
is at a point whose range is Z, assuming the wind, atmosphere, and
projectile weight factors to be correct, onl' may work back to determine
the actual powder velocity.
592. For the correlation Qf the observations of the terrestrial observers
the deviation board, plate 476, is the best device. This board
was devised by Col. Pirie in France and later modified and simplified
to two sheets of paper and a triangle or T square, plate 477. The
board is an adaptation of the French system, which is as follows: A
sheet of paper is stretched over a plate of zinc and the point T, target,
is located about in the center, figure 1, plate 478. The positions of
the three observers, 0 1, 0" and 0" are then k>cated accurately, either
on or off the board, usually off. With these points as centers, two.
arcs are drawn for each. A line through 0 1 and,T locates zero for that
observer; the arcs are graduated on each side of zero; so also for 0,
and 0.. When the observers at these three points observe a burst it
is plotted as shown; e. g., 0, reports the burst 5 mils to the right; a line
is drawn through the 5-mil points on the two arcs whose center is 0,.
Similar lines are drawn for 0 1 and 0" according to their reports. The
burst is supposed to be in the center of the resultant triangle.
593. In the French Army the aerial observer USl'S a photograph of
the region on which the target is located; this photograph is carefully
ruled in checker-board faShion. The observer locates the burst on his
photograph and reports the distance to the right, lp,ft, over, or under.
The battery commander plots these reports on a sheet ruled as in figure
2, plate 478. It will be noted that the up and down lines are convergent;
they pass through the battery position. It will he noted also
that these lines are labeled both in yards and in angular units for the
quick translation of the observations. The horizontal lines are likewise
labeled in terms of distances and angles. It may be well to
mention here that one car of the standard A. E. F. design, plate 479,
was fitted to serve as a fire-control car. Plans were made to supply
these cars for service in France, but on advice from France that they
were not desired the plan was abandoned.
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