Fig. 58.
Fig. 58.
Fig. 58.
A. If this were always done, the azimuth indicator-plate or subscale would have to be directly under the muzzle of the gun—a very awkward and inconvenient place. These azimuth sub-scales are therefore placed on the side, and when the gun or mortar points south the subscale points at zero on the azimuth-circle.
Q. Give some rules for caring for the azimuth instrument.
A. Never allow any of the leveling-screws to become so tight that they cannot beeasilyturned by hand. When setting the instrument up over a concrete floor make little holes in the concretefor the points of the tripod-legs to set in. Never wipe the lenses with anything having the least sign of dirt or grit upon it. A perfectly clean chamois is always best. See that all screws are firmly clamped before putting the instrument away in the wooden carrying-box. In removing it from the box, pick it up by placing the hands underneath the worm-gear. Never clamp the instrument too tightly to the tripod-head. After the instrument is once leveled avoid jarring or leaning upon it.
Q. In case the azimuth-instrument will not stay level after performing the usual operation of leveling, how do you adjust the levels?
A. Set one level parallel with two opposite leveling-screws, and bring the bubble to the center by turning these two screws either both inward or both outward. Reverse the telescope through 180°. If the bubble is not in the center, this level is out of adjustment. Now correct one half of the error by using the small steel pin on the little adjusting-screws on the levels, and the other half by using the two opposite leveling-screws referred to above. Now turn the telescope 180° again. If it is still out of level, continue the above method of correction until, on reversing the telescope, no change in motion of the bubble can be observed.
Q. Give a rule for finding the least count of a vernier.
A. Divide the value of the smallest division on the limb or main scale by the number of divisions there are on the vernier. The result is equal to the least count on the vernier.
Q. How would you focus the telescope.
A. Focus the eyepiece until the cross-wires appear rough.
Then turn the telescope on some distant object and focus the objective by means of the focusing-knob until the intersection of the cross-wires remains on the same point, when the eye is moved up and down and to right and left.
Q. Set up the azimuth instrument over a given point; level, orient, and focus it.
(This should be practiced frequently.)
Examples.—I. The number of divisions on a vernier = 25. The value of the smallest division on the main scale = 25 yards. What is the least reading of the vernier?
Ans.25 ÷ 25 = 1 yard.
II. The value of the smallest division on the main scale of the mercurial barometer = 1/10 of an inch. The number of divisions on the vernier = 10. What is the least count of the vernier?
Ans.1/10 ÷ 10 = 1/100 of an inch.
Note.—The following scheme for accurately counting seconds has been found valuable to gunners who have no stop-watches; it is also used by many photographers in timing pictures. When ready to start to count the time of flight, for example, trail your gun or instrument on the target, stop traversing, and count to yourself: Oneone thousand, twoone thousand, threeone thousand, fourone thousand, etc., until finished, sayingone thousandafter each number. The time required by the average man to say oneone thousandor eightone thousandis equal to one second. With but little practice a gunner can be trained to count as high as 20 seconds accurately. In such cases stop-watches are not necessary.
Q. Point out or describe the following parts of the Whistler-Hearn plotting-board: The table, the azimuth-circle, azimuth graduations for primary and secondary stations, base-line arm, base-line plate, primary station, secondary station, primary arm, secondary arm, directing-gun arm, directing-gun azimuth-circle, base-line verniers, directing-gun vernier, base-line-arm verniers, azimuth-indices for primary and secondary stations, auxiliary arm, connecting-bar, clamp for arm index-clamp, gun-arm clamp, reading-opening for directing-gun azimuth-circle, index for gun azimuth-circle, speed-scale for range, speed-scale for azimuth or azimuth-travel devices, range correction-device, azimuth correction-device, micrometer, the "targ, tally dials."
A. See Figs. 59, 60, 61, and 62. These figures show by steps the "evolution of the Plotting Board."
SIMPLE PLOTTING-BOARD.Fig. 59.
SIMPLE PLOTTING-BOARD.Fig. 59.
SIMPLE PLOTTING-BOARD.
Fig. 59.
PLOTTING-BOARD WITH GUN-ARM.Fig. 60.
PLOTTING-BOARD WITH GUN-ARM.Fig. 60.
PLOTTING-BOARD WITH GUN-ARM.
Fig. 60.
Q. Describe how to obtain the range of a target from the primary or secondary station when the azimuth-angles from the primary and secondary stations are given to you.
A. First: Set the auxiliary-arm index to read the number of even degrees the target is from the secondary station, setting the arm-clamp in the V-shaped notch on the azimuth-circle corresponding to that number of degrees.
THE MODERN PLOTTING-BOARD.Fig. 61.
THE MODERN PLOTTING-BOARD.Fig. 61.
THE MODERN PLOTTING-BOARD.
Fig. 61.
Second: Set the index-disc to read the hundredths by turning the index-knob and clamp the index. The auxiliary arm is now set; therefore the secondary arm is set automatically in azimuth by virtue of its always remaining parallel to the auxiliary arm.
Third: Set the primary arm to read the number of degrees and hundredths the target is from the primary station. (The point of intersection of the fiducial or bevel edges of the primary and secondary arms is the position of the target on the plotting-board.)
Fourth: Slide the metal intersection-block or "targ" along the secondary arm until it touches the edge of the primary. The range in yards can now be readily read on the scales marked on these arms. (Fig. 62.)
WHISTLER-HEARN PLOTTING-BOARD. (Perspective Drawing. Secondary and auxiliary arms should be parallel.)Fig. 62.
WHISTLER-HEARN PLOTTING-BOARD. (Perspective Drawing. Secondary and auxiliary arms should be parallel.)Fig. 62.
WHISTLER-HEARN PLOTTING-BOARD. (Perspective Drawing. Secondary and auxiliary arms should be parallel.)
Fig. 62.
Q. How are the range and azimuth for the directing-gun obtained for the same target?
A. Move the gun-arm up to the intersecting edge of the targ, and read the range from the scale on the gun-arm. The degrees of azimuth are read through the reading-opening, and the hundredths are read on the index-disc for the gun-arm.
Q. Suppose the range must be corrected for, say, 150 yards more, and the azimuth for 1·78 degrees less, how can the corrected range and corrected azimuth be automatically read on the gun-arm?
A. Turn the pinion on the gun-arm to move the scale of the range correction-device until 2150 is set. (Thezeroof this scale = 2000.) (By doing this it is readily seen that the gun-arm range-scale is just 150 yardsnearerthe gun center; consequently all ranges read on this scale will be 150 yards more than if the range correction-device were at zero.) The azimuth correction is set by turning the micrometer until the number of even degrees of the azimuth correction (in this case one degree less) is read on the main scale, and the hundredths on the micrometer. (Thus it is seen that the gun-arm will read as many degrees and hundredths more or less than the true azimuth as the number of degrees and hundredths of the azimuth correction determined.)
Note.—Having determined by the ballistic board the range and azimuth corrections, they will usually answer for some time and thus avoid continual setting of these corrections on the gun-arm.
Q. What is the object of the travel-devices for range and azimuth correction on the gun-arm?
A. These are to determine the amount of change of range and azimuth between each observation of the target. The results thus obtained are given to the range- and deflection-board operators, who use it in finding the total range correction and the total azimuth correction.
Q. What are all plotting-boards principally used for?
A. For finding the position of a target whereby the range and the azimuth of it from any other point (as a directing-gun of a battery) can be determined.
Q. What is meant by the scale of a plotting-board?
A. By the scale of a plotting-board is meant, one inch on the board is equal to one, two, or so many yards on the ground; e.g., a scale of "one inch equals 300 yards" means, one inch distance on the board equals 300 yards on the ground.
Q. How can you determine the distance between two points on a plotting-board?
A. By using the range-arm that is constructed for the scale to which the board is drawn, setting the zero on one point and reading the number of yards on the arm where the point cuts the scale-edge.
Q. How is the longitudinal deviation measured on the plotting-board?
A. Measure the distance from the gun to the target, and from the gun to the splash. Subtract the lesser from the greater, and this will be the longitudinal deviation, according to the meaning given in drill regulations.
Q. How is the lateral deviation measured?
A. Read the azimuth of the target and splash from the directing-gun. Subtract the lesser from the greater: result = lateral deviation. If the azimuth to the target be greater than that to the splash, it is seen that the deviation will be to the left andvice versa.
Q. How are open sights on rapid-fire guns used?
A. The same as on small-arm pieces; i.e., the range in yards or elevation in degrees and minutes is set on the rear sight according to how the sight is graduated, and the gun is elevated and traversed until the target, front sight, and rear sight all come in line.
Q. Describe the 5" R.F. sight.
A. It consists of a sight-bar graduated in degrees and minutes (lowest reading being six minutes), with a sliding scale at the top for deflection right or left, the deflection-scale reading to three minutes. A range-drum is also geared to the sight-bar, and moves with it in such a manner that when the piece has a certain elevation it will shoot to a distance equal to the range on the drum. This avoids using any range-table.
Q. Describe the 6-pdr. R.F. sight.
A. A simple bar-sight graduated to yards with a deflection-scale reading to three minutes.
Q. How is the deflection-scale set on open sights when it is desired to fire to right or left?
A. To fire right, move the peep-hole to the right; to fire left, move the peep-hole to the left.
Q. From what line is all elevation measured?
A. From the axis of the bore. (See Fig. 63.)
Fig. 63.
Fig. 63.
Fig. 63.
Q. Define sight elevation.
A. The angle between the axis of the bore before firing and the line of sight. (See Figs. 63 and 64.)
Q. In case shot strikes to the right or left, and as gunner you had the sight on the target when the shot struck, how could you correct your error with a telescopic sight or open sights?
A. Stopping traversing at the instant shot strikes, move the vertical hair rapidly to the splash. The sight is now corrected for the error, and its setting will be correct for the next shot.
The Frame.—The outside frame, or box, of the instrument.
The Board.—That upon which the charts are pasted.K-K.
SIGHT SET FOR "QUADRANT ELEVATION"SIGHT SET FOR "SIGHT ELEVATION"(EXAGGERATED DIAGRAMS.)Fig. 64.
SIGHT SET FOR "QUADRANT ELEVATION"SIGHT SET FOR "SIGHT ELEVATION"(EXAGGERATED DIAGRAMS.)Fig. 64.
SIGHT SET FOR "QUADRANT ELEVATION"
SIGHT SET FOR "SIGHT ELEVATION"
(EXAGGERATED DIAGRAMS.)
Fig. 64.
The Ruler.—The balance wooden strip to which the metal scale and slides are attached.X-X.
The Scale.—The fixed graduated scale on the ruler.m-m.
The Bar.—The metal rod or bar which slides on thetopof the scale.
The Register.—The fixed point in the center of the bar.a.
The Trammel.—The pointer which slides on the bar.b.
The Pointer.—The pointer at the top of the trammel.
The Index.—The lower point on the trammel.
Normals.—The straight vertical lines in each set of curves.
The String.—The cord on the right side of the board used in determining travel.
The Travel-scale.—Scales for setting the string.
Prediction-scale.—Vertical lines on the right side of the board, used in determining the travel during the observing interval.
Adjust the ruler by means of the adjusting-screw on the left, so that its upper edge coincides with the parallel lines on the board.
The bar is clamped by means of the screw near the left end of the ruler.
The bar must be held firmly while moving the trammel. In making corrections for artillery fire the following data, as obtained at the opening of the action, will usually suffice for the entire action.
Density of the air,Velocity of the wind,Azimuth of the wind,Height of tide.
Density of the air,Velocity of the wind,Azimuth of the wind,Height of tide.
The range effects and deviating effects of the wind must be obtained for each shot. Tide should be changed at least every half-hour. As soon as the density of the air is ascertained the computer will insert a pin, or set the pointer at the top of the corresponding curve. The same will be done for height of tide.
The muzzle velocity to be used for the first shot will be marked in a similar manner as directed by the range officer. The wind-component device having been set for the azimuth and velocity of the wind and the azimuth of the target, the computer will note the reference-number and set the pointer at the top of the wind-curve having that number.
THE RANGE-BOARD.Fig. 65.
THE RANGE-BOARD.Fig. 65.
THE RANGE-BOARD.
Fig. 65.
As soon as he receives the travel reference-number he will set the string accordingly, using the scale for theobserving intervalused.
To determine correction.—As soon as the approximate range is received, the computer sets the ruler for the range and the index at zero; he then slides the trammel to the left until the pointer is opposite the atmosphere curve as indicated by the pointerse,f,g, etc., holding the bar in place with the left hand. He then slides the bar until the pointer is at normal for atmosphere; this completes the correction for atmosphere.
He then proceeds in the same manner forwindandtide, always sliding the trammel until the pointer is at the indicated curve, holding the bar in place with the left hand and then sliding the bar until the pointer is at normal.
If the muzzle velocity is normal, no correction is made for velocity. If, however, the muzzle velocity is not normal, he makes a correction for muzzle velocity in a similar manner as for other data.
The above corrections are made before the travel is received. The computer clamps the bar and then waits until he receives the travel.
As soon as the travel is received, he sets the string, slides trammel until the pointer is opposite the string, unclamps the bar and moves it until the pointer is opposite the normal; this adds the correction for travel during the time of flight.
He then notes the total travel during the observing interval, which is indicated by the position of the string on the travel-scale corresponding to the observing interval used. He slides the trammel so that the pointer will be at the vertical line corresponding to the total travel during the observing interval, and then slides the bar to the normal; this adds the travel during the observing interval. He now clamps the bar.The register now indicates the total correction to be applied to the arm.
Trial-shots.—The gun is laid so that the shot should have a certain range, all corrections having been determined as described above, except of course that for travel.
The bar is set with the index at zero, and the trammel is set at the muzzle velocity used in the computation for the shot.
The gun is fired and the range of the shot is plotted. The range officer determines how much the shot has fallen short or gone beyond, and announces the result as plus or minus so many yards. The computer moves the bar plus or minus the number of yards announced, using the scale for this purpose.
The pointer now indicates the muzzle velocity to be used in computing the next shot. The velocity pointer is moved accordingly.
If a second trial shot is used, the corrections are computed as before, using, however, the new muzzle velocity as determined from the first shot.
In determining a second corrected muzzle velocity the bar should be moved for but half the longitudinal deviation of the shot from the expected range; the pointer then marks the velocity to be used for the next shot.
In case a third trial shot is used the process is the same except that the bar is moved for but one third of the longitudinal deviation.
The curves are given for every ten yards of range, for every ten per cent of weight of air, and for every ten miles of wind, etc.
For conditions in which the values lie between these readings, the trammel can readily be set by the eye sufficiently close for all practical purposes.
Example: Range 7000; atmosphere 20; wind 70; velocity 2260; travel 400; tide +10. Find the correction to be applied to the gun-arm.
Solution:
I.Set rulerXXat 7000 on scaleKK.II.Set pointeraat 2000 on scaleMM.III.Set pointereat 20;fat 70;gat +10;hat2260, stringccat 400 on 20-second intervalline, and scaleddsuch that the number400 cuts the intersection of the string with rulerXX.IV.Set pointerbat 16 (atmosphere normal);move slideztillbcuts the 20 curve of atmosphere.V.Setbat 50 (zero wind) and slideztillbcutsthe 70 curve.VI.Setbat 0 tide and slideztillbcuts +10.VII.Setbat 2200 I. V. and slideztillbcuts 2260.VIII.Setbat 400 on scaleddand slideztillbcuts300 (normal) on scaledd.
The range correction is now found on scalemmopposite pointera. This number is now set on the gun-arm of the plotting-board and each next plotted position will read on the range-scale of the gun-arm just that many yards more or less than the true range, i.e., the corrected range.See Fig. 65.
The range correction is now found on scalemmopposite pointera. This number is now set on the gun-arm of the plotting-board and each next plotted position will read on the range-scale of the gun-arm just that many yards more or less than the true range, i.e., the corrected range.See Fig. 65.
Platen.—The rectangular sliding frame.
Wind-arm.—The arm pivoted to the board on the left of the platen.
Wind-component Scale.—The scale above the movable end of the wind-arm.
Drift-curve.—The curved edge of the metal plate attached to the left end of the platen.
Travel-arm.—The arm pivoted on the platen.
Azimuth Correction-scale.—The sliding scale below the platen.
Deflection-scale.—The fixed scale immediately above the azimuth correction-scale.
THE DEFLECTION-BOARDFig. 66.
THE DEFLECTION-BOARDFig. 66.
THE DEFLECTION-BOARD
Fig. 66.
Travel-scale.—A scale for making corrections for angular travel of the target; there are two, one below the azimuth correction-scale and one on the platen.
"T" Square.—The sliding "T" square having the time graduations at one edge, corresponding to given ranges.
Place the travel-scale on the platen in the lower or upper position according as the observing interval is 10 or 20 seconds.
As soon as the wind-component device is set note the deflection reference-number indicated, and set the wind-arm to the corresponding reading on the wind-component scale.
Set the platen so that the point of the drift-curve corresponding to the given range will be accurately over the right-hand edge of the wind-arm.
As soon as the reference-number indicating theangular travelof the target during the observing interval is announced, set the travel-arm (right edge) for that travel by the travel-scale on the platen and set the azimuth correction-scale for the same travel by means of the travel-scale below it.
Set the "T" square so that the point of its scale corresponding to the given range will be accurately over the right edge of the travel-arm.
The azimuth correction to be applied to the gun-arm in all cases is then read from the azimuth correction scale at the bevel edge of the "T" square.
When Case I or II is being used the deflection to be sent to the guns is read from the deflection-scale at the bevel edge of the "T" square.
After the second observation the corrected range determined is used in setting the platen and "T" square.
See Fig. 60.
Q. How do the divisions on the azimuth-subscale and the deflection-scale of the sights compare with one another?
A. They are equal—the least reading on the former = 5 hundredths, and on the sight-scale one point or division = 5 hundredths or 3 minutes.
Q. How are the predicted range and predicted azimuth obtained?
A. It is now, under the new system of fire direction, obtained by means of the travel correction on the range correction and azimuth correction-board. If these new boards are not yet issued, the use of a range-keeper's range prediction-scale and a gunner's azimuth prediction-scale determines them at the gun. The old method was by plotting several positions of a target on the plotting-board and using a prediction-ruler, whence thepredicted pointwas obtained.
Q. Define quadrant elevation.
A. The angle between the axis of the bore before firing and the horizontal plane. (See Figs. 63 and 64.)
Q. What is the difference between quadrant and sight elevation?
A. Where the gun is above the target, sight elevation equals quadrant elevation plus the angular depression of the target. Where the gun is below the target, sight elevation equals quadrant elevation minus the angular elevation of the target.
Q. How is the gunner's quadrant used?
A. It is used principally in giving elevation to mortars by first setting the movable arm such that the knife-edged tooth engages in an even-degree mark on the rack, and by moving the sliding level to read the exact number of minutes. Then it is placed on its seat at the breech, being careful to see that the arrow points in the direction of the line of fire, and by elevating or depressing the piece until the bubble comes in the middle the mortar or piece will be set at the elevation set on the quadrant. (See Fig. 67.)
THE GUNNER'S QUADRANT.Fig. 67.
THE GUNNER'S QUADRANT.Fig. 67.
THE GUNNER'S QUADRANT.
Fig. 67.
Q. Point out the following parts of the telescopic sight: Telescope, objective, eyepiece, erecting-prisms, trunnions, leveling-lug, leveling-screw, cross-level, elevation-arc, elevating-screw, vernier, focusing-collar, deflection-screw, deflection-scale, micrometer, disc, and telescope-level. (See Fig. 68.)
THE TELESCOPIC SIGHTMODEL 1898.Fig. 68.
THE TELESCOPIC SIGHTMODEL 1898.Fig. 68.
THE TELESCOPIC SIGHT
MODEL 1898.
Fig. 68.
Q. How is deflection set on it?
A. By moving the deflection-screw the vertical cross-wire moves.
Q. How is deflection set to fire right and to fire left?
A. Move the vertical hair to the right to fire left, move it to the left to fire right, by turning the deflection-screw.
Q. How is elevation set on it?
A. Set the zero of the vernier opposite the mark on the limb representing the number of even degrees of the given elevation. Then turn the micrometer-disc by turning the elevation-screw until the given number of minutes is read on it. The sight is then set on the trunnion-bracket and the piece elevated till the bubble comes in the middle for quadrant elevation or till the horizontal cross-hair cuts the water line of target for sight elevation. The gun then has the elevation set on the sight.
Q. What is the lowest reading of the vernier on the elevation-arc?
A. Two minutes.
Q. What is the lowest reading of the deflection-scale?
A. Three minutes.
Q. Why is it necessary to elevate the gun till the bubble on the telescope-level comes in the middle, to set the gun for quadrant elevation?
A. Because by definition quadrant elevation is the angle between the axis of the bore and the horizontal plane, and when the bubble is in the center of the level the telescope is horizontal and the axis of the gun makes an angle with it equal to the elevation set on the arc.
Q. Name and point out the following parts of the rapid-fire sight: Telescope, objective, eyepiece, interior and exterior deflection-scales, micrometer-head, deflection-screw, open sights, dew-cap, lugs, and thumb-screws.
A. See Fig. 70.
Q. What is one point on the deflection-scale equal to at the target?
A. One five-hundredth of the range in yards; thus onepoint equals 2 yards at 1000 yards, 4 yards at 2000 yards, and so on.
Q.Example: The range is 5000 yards, and the drift for that range is found in the range-table to be 12 minutes; how would you set your deflection-scale on the telescopic sight?
A. "Fire left" 12 minutes, or 4 points.
Q. Why?
A. Because drift in our service is always to the right, and to overcome this drift and make the projectile hit the target we will haveto fire to the leftthis 12 minutes due to drift.
Q.Example: The range is 5000 yards, and the component of the wind perpendicular to the line of fire is 20 miles, giving from the range-table correction for drift equal to 12 minutes and wind 6 minutes. The wind is blowing from right to left. How would you set your sight?
A. "Fire left" 6 minutes.
Q. Why?
A. Because, as shown above, the drift alone would require the sight to be set at "Fire left" 12 minutes, and if the wind correction is 6 minutes and is blowing from right to left, to overcome this wind and make the projectile hit the target we would have to "Fire right" 6 minutes. Therefore, if the total setting of the sight is to be "Fire left" 12 minutes plus "Fire right" 6 minutes, the final or resultant setting should be "Fire left" 6 minutes.
Note.—The corrections for wind and drift are usually found at the same time from a chart, correction-board, or table.
Q.Example: The time of flight is 10 seconds (this is found from the gun commander's range-table, knowing the range); how would you determine the correction for travel with a telescopic sight?
A. Set the sight at zero. Traverse the gun until the vertical hair cuts the target. Signal: "Stop traversing," and count the number of seconds time of flight (10), moving by the righthand the deflection-screw, to keep the vertical hair on the target. When 10 seconds are counted stop turning the deflection-screw. Where the vertical hair now rests is the correction for "travel during time of flight." Since to "Fire left" we move the vertical hair to theright, this correction for travel found will have to be set for "Fire left," or on the other side of the scale, if the target is moving fromrighttoleft. If it is moving fromlefttoright, the correction found will have to be set "Fire right." In other words, always set the cross-hair in the opposite direction from the motion of the vessel in making the correction for travel. This also applies to open sights.
Q.Example: If you were given the range, a gun commander's range-table, a correction for wind and drift equal to "Fire left" 9 minutes, and the target were moving from right to left, how would you proceed to determine the setting of your sight?
A. First, determine by the above method the correction for travel during time of flight (time of flight being found in the gun commander's range-table). Set this on the sight. Suppose it were "Fire left" 3 minutes.
Second, use this position of the vertical hair as a new zero, and move the vertical hair to "Fire left" 12 minutes. That is, "Fire left" 3 minutes plus "Fire left" 9 minutes equals "Fire left" 12 minutes.
If the travel had been "Fire right" 3 minutes, then by moving the scale "Fire left" 9 minutes, the final setting of the sight would have been "Fire left" 6 minutes.
Q. From the table on page 129 find the number of yards 3 points on the telescopic sight are equal to at 7000 yards range.
A. 18 yards.
TELESCOPIC SIGHT. (Model 1898.)Fig. 69.
TELESCOPIC SIGHT. (Model 1898.)Fig. 69.
TELESCOPIC SIGHT. (Model 1898.)
Fig. 69.
3-INCH RAPID-FIRE GUN-SIGHT.Fig. 70.
3-INCH RAPID-FIRE GUN-SIGHT.Fig. 70.
3-INCH RAPID-FIRE GUN-SIGHT.
Fig. 70.
2. Point or describe the location of the following parts of the telescopic sights, Model 1904:
Eye-lens cover.Dial.Focusing ring.Peep-sight.Eye-end telescope clamp.Deflection worm knob.Telescope tube.Elevation rack.Cell-end telescope clamp.Objective shutter.Cradle.Cross sight.Yoke-cap.Deflection-pointer bracket.Fulcrum.Elevating wheel and hub.Sight-bracket.Plug connection for lamps.Lamp-holder for deflection scale.Range drum.Gear-case cover and cover for range drum.Telescope lamp-holder.Sight-shank elevation-scale.Elevation-guide.Sight-arm.Yoke-shaft.Bearing for yoke.Yoke.Lamp-bracket for range drum and elevation-scale.Elevation worm.Focusing sleeve nut.Deflection scale.Elevating gear-shaft.Deflection worm.Eye-lens.Field lens.Cross-wire ring.Cross wires.Erecting prisms (Porro).Objective.
Eye-lens cover.Dial.Focusing ring.Peep-sight.Eye-end telescope clamp.Deflection worm knob.Telescope tube.Elevation rack.Cell-end telescope clamp.Objective shutter.Cradle.Cross sight.Yoke-cap.Deflection-pointer bracket.Fulcrum.Elevating wheel and hub.Sight-bracket.Plug connection for lamps.Lamp-holder for deflection scale.Range drum.Gear-case cover and cover for range drum.Telescope lamp-holder.Sight-shank elevation-scale.Elevation-guide.Sight-arm.Yoke-shaft.Bearing for yoke.Yoke.Lamp-bracket for range drum and elevation-scale.Elevation worm.Focusing sleeve nut.Deflection scale.Elevating gear-shaft.Deflection worm.Eye-lens.Field lens.Cross-wire ring.Cross wires.Erecting prisms (Porro).Objective.
A. See Figs. 71 and 72.
Fig. 71.3-INCH TELESCOPIC SIGHT, MODEL OF 1904.
Fig. 71.3-INCH TELESCOPIC SIGHT, MODEL OF 1904.
Fig. 71.
3-INCH TELESCOPIC SIGHT, MODEL OF 1904.
Fig. 72.3-INCH TELESCOPIC SIGHT, MODEL OF 1904.
Fig. 72.3-INCH TELESCOPIC SIGHT, MODEL OF 1904.
Fig. 72.
3-INCH TELESCOPIC SIGHT, MODEL OF 1904.
Table of Values in Yards of Points of Deflection.
Min.3691215Points.12345Range.Value of Points in Yards.10001234520002468103000369121540003691215500048121620600051015202570006121824308000714212835900081624324010000918273645
Note.—This table is onlyapproximate. It is true within 1 yard, which is sufficiently accurate for all firing under Case II.
Q. Where is the sight placed under cases one, two, and three?
A. On the trunnion for case one, to give both elevation and direction. On the sight standard for case two, to give direction only (quadrant elevation is set by the elevating-arc). It is not intended to be used at all in case three, but, of course, it could where the quadrant elevation is to be set by the sight instead of by the elevation-arc. It will then have to be placed on the trunnions.
Q. Define cases one, two, and three.
A. Case one, where direction and elevation are given by the sight on the trunnion. Case two, where direction is given by the sight, and elevation by the quadrant or elevating-arc. Case three, where direction is given by the azimuth-circle, and elevation by the quadrant or arc.
Q. What is the difference between the axis of the bore and the line of departure?
A. The jump. (See Fig. 63.)
Q. What is the line of sight?
A. Line joining the target, the point of the front sight and the peep of the rear sight; or with telescopic sights, the line joiningthe target and the intersection of the vertical and horizontal hairs in the sight. (See Fig. 63.)
Q. Define time of flight.
A. The time it takes the projectile to leave the bore till it strikes.
Q. What is atangent?
A. A straight line which touches but one point on the circumference of a circle and is perpendicular to the radius at that point.
Q. Define angle of fall.
A. It is the angle which the tangent to the trajectory at the point of impact makes with a line parallel to the line of sight at this point.
Q. What is the line of departure?
A. The prolonged axis of the bore at the moment the projectile leaves the muzzle.
Q. What is the line of fire?
A. The prolonged axis of the bore before the gun is fired.
Q. What is the axis of the bore?
A. The line passing through the centre of the bore from breech to muzzle.
Q. What is the angle of departure?
A. The angle included between theline of departureand the horizontal plane.
Q. Define drift.
A. It is the deviation due to the rifling in the gun to the right or left of the vertical plane passing through the axis of the bore, or plane of fire. It is always to the right in the U. S. service.
Q. To what in a telescopic sight does the front sight on an open sight correspond?
A. The intersection of the cross-hairs.
Q. To what does the rear sight correspond?
A. The eye-lens.
Q. What is the trajectory?
A. The path of the projectile in the air.
Q. How is the velocity of the wind determined?
A. By the anemometer. First take the reading of the discson the anemometer and note the time. After six minutes have elapsed read the scales. Take the difference of the scales and multiply by 10, which gives the velocity. (See Fig. 73.)
For example: Suppose at 10:05A.M.the reading is 62 miles, and at 10:11A.M.the reading is 63 miles. If in six minutes it goes one mile, in sixty minutes it will go ten times, or ten miles per hour.