Q. From the following gun commanders' range-scale find the time of flight, sight elevation, and quadrant elevation for 4120 yards range.
GUN COMMANDERS' RANGE-SCALE. I. V. 2200. 8-inch B. L. R. Smokeless powder.
---------------------+---------+-----------------------+------------------- Quadrant Elevation. | | Sight Elevation. | ----------+----------+ Range. +------------+----------+ Time of Flight, | | | | | Seconds. Degrees. | Minutes. | | Degrees. | Minutes. | ----------+----------+---------+------------+----------+------------------- +4 | 16 | 4100 | -1 | 3 | 6-1/5 +4 | 18 | 4120 | -1 | 1 | +4 | 20 | 4140 | -0 | 58 | +4 | 23 | 4160 | -0 | 56 | 7-2/5 +4 | 26 | 4180 | -0 | 54 | +4 | 28 | 4200 | -0 | 51 | +4 | 31 | 4220 | -0 | 49 | 8-2/5 ----------+----------+---------+------------+----------+-------------------
[Illustration: ELECTRICAL DEVICE FOR OPERATING ANEMOMETER STOP-WATCH. FIG. 78.]
A. 6-1/5 seconds, about; 1° 1' minus (depression); 4° 18' plus (elevation).
A. This is merely a graphic table by means of which the reference-numbers to be recorded on the atmosphere-aeroscope indicator can be determined from the readings of the barometer and thermometer. The arguments are barometer and thermometer readings, and the reference-numbers are indicated by diagonal lines. The thermometer axis is horizontal and the barometer axis is vertical. To increase the ease and rapidity of reading the barometer scale is graduated on a movable T square.
The method of construction is shown in Fig. 79.
_Operation._--Set the T square for the thermometer reading and note the diagonal line which intersects the fiducial edge of the T square the nearest to the barometer reading. The atmosphere dial is graduated to ½ per cent. The reading of the board should be taken to the nearest half reference-number.
[Illustration: ATMOSPHERE BOARD FIG. 79.]
Q. Point to the following parts of the Mortar Gun-arm:
Movable gun-arm. Yards range. Overlap. Elevations. Time of flight. Zones.
Q. Describe the set-forward ruler and explain its use.
A. First find the travel in yards per minute. Set the pointer (_a_) on the slide (_b_) at the number of yards on the scale of "yards travel per minute (_c_)." Then on gun-arm get time of flight for that point. The "set-forward point" will be the reading opposite time of flight on the scale of "yards travel during time of flight +1 minute (_d_)." (See Fig. 81.)