FOOTNOTES:[1]Sphero-hexagonal is no longer used.[2]The minimum charge for mortars is, according to an endorsement from the Chief of Ordnance, 18 lbs.
[1]Sphero-hexagonal is no longer used.
[1]Sphero-hexagonal is no longer used.
[2]The minimum charge for mortars is, according to an endorsement from the Chief of Ordnance, 18 lbs.
[2]The minimum charge for mortars is, according to an endorsement from the Chief of Ordnance, 18 lbs.
Q. Define yarn, strands, jaws of rope, short- and long-jawed rope, guys, spun-yarn, marlin, standing rigging, running rigging, and a bight.
A. Yarn are called threads of hemp or other fibrous material which compose a rope.
Strand is a number of yarns twisted together.
Jaws of rope are the interstices between the strands of rope.
Short-jawed rope is a rope tightly laid up together.
Long-jawed rope is a rope loosely laid up together.
Guys are stationary ropes to hold spars, such as pry-poles, shears, etc., from falling.
Spun-yarn is made by twisting together very loosely two or more well-tarred yarns. It is used for serving, seizings, stops, etc., and is very pliable.
Marlin is also made of tarred yarns, but is tightly twisted and is much harder and smoother than spun-yarn.
The bight of a rope is any part not an end.
A bight of a rope is formed by bending or doubling the rope so as to form a loop.
Standing rigging are those ropes which are stationary.
Running rigging are those which run through blocks or pulleys. (See Figs. 45 and 46.)
Q. Explain the difference between hawser-laid rope and cable-laid rope.
A. Cable-laid rope is composed of nine strands, and is made by first laying up three ropes of three strands each with the sun, and then laying the three ropes together into one, against the sun. Hawser-laid rope must be coiled with the sun. Hawser-laid rope is a right-handed rope, and cable-laid is therefore left-handed. (See Fig. 44.)
Q. How is the size of the rope denoted?
A. The size of the rope is always denoted in inches and fractions, and is measured on the circumference. (See Fig. 44.)
Q. (a) How do you worm a rope? (b) Why?
A. (a) Worming a rope is filling up the divisions between the strands by passing spun-yarn along them. (b) This is to render the surface smooth for parceling and serving. (See Fig. 44.)
Q. (a) How do you parcel a rope? (b) Why?
A. (a) Parceling rope is wrapping narrow strips of canvas about it, well tarred, put on with the lay of the rope. (b) To secure it from being injured by rain-water or to prevent chafing or cutting of a rope when a strain is brought against a rough surface or sharp edge. (See Fig. 44.)
Fig. 44.
Fig. 44.
Fig. 44.
Q. (a) How do you serve a rope? (b) Why?
A. (a) Serving is the laying on of spun-yarn or other small stuff in turns around the rope close together, and hove taut by the use of a serving-board for small rope and mallet for large rope. Small ropes are sometimes served without being wormed, as the crevices between the strands are not large enough to makethe surface very uneven. But a large rope is always wormed and parceled before being served. (b) The service is put on against the lay of the rope. (See Fig. 44.)
Q. (a) How do you whip a rope? (b) Why?
A. (a) Whipping is securing the end of a rope with twine. (b) To prevent it from fraying out. (See Fig. 44.)
Q. Make the following knots and give the use of each: A square knot, a bowline, single sheet-bend (weaver's knot), double sheet-bend, rolling hitch, round turn and two half-hitches, clove-hitch, catspaw, blackwall hitch, sheep-shank, a marlinspike-hitch.
A. See Fig. 45. This figure illustrates the manner of making these knots. Their uses are as follows:
Square knot: A quick knot to tie two ends of rope together that will not slip.
Bowline: To form a temporary eye at end of a rope. This knot can be easily made and remembered by making a marlinspike-hitch and putting the loose end of the bowline through the loop where the spike would go.
Single and double sheet-bend: To tie two ropes together. These knots do not jam. When one rope is smaller than the other the double sheet-bend is always used, making the double turn with the smaller rope.
Rolling hitch: For shifting the fall from one end of a windlass to the other.
Round turn, two half-hitches, and clove-hitch: These are very useful in securing the guys of a gin to the stakes, etc.
Catspaw: To apply the purchase or tackle to the fall of another.
Blackwall hitch: To fasten the end of a rope to a hook when there is a steady strain on rope.
Marlinspike-hitch: Very useful in putting on lashings, etc.
Q. What is a strap or sling, and what is its use?
A. A strap or sling is formed by knotting or splicing together the ends of a short strand of rope. It is used for hooking tackles into.
KNOTSFig. 45.
KNOTSFig. 45.
KNOTS
Fig. 45.
Fig. 46.—Short Splice.
Fig. 46.—Short Splice.
Fig. 46.—Short Splice.
Fig. 47.—Long Splice.
Fig. 47.—Long Splice.
Fig. 47.—Long Splice.
EYE SPLICEFig. 48.
EYE SPLICEFig. 48.
EYE SPLICE
Fig. 48.
Q. What is a splice?
A. Splicing is putting the ends of rope together by opening the strands and placing them one into the other, or by putting the strands of the rope between those of the bight.
Q. How is an eye-splice made?
A. Unlay the end of the rope for a short distance and lay the three strands upon the standing part, so as to form an eye. Put the first end through the strand next to it. Put the second end over the strand and through the second, and then put the remaining end through the third strand on the other side of the rope. Taper them as in the short splice by dividing the strands and sticking them again. The eye-splice is used to form a permanent loop in the end of a rope. (See Fig. 48.)
Q. How do you make a short splice?
A. Unlay the strands for a convenient length; take an end in each hand, place them one within the other, and draw them close. Hold the end of one rope and the three strands from the other in the left hand; if the rope is large, stop them down to it with a rope yarn. Take the middle strand, which is free, pass it over the strand which is first next to it, then through under the second and out between the second and third from it, and then haul it taut. Pass each of the six strands in the same manner, first those of one end and then those of another. The same operation may be repeated with each strand, passing each over the third strand from it, under the fourth and through; or, as is more usual, after the ends have been stuck once untwist each strand, divide the yarns, pass one half as above described, and cut off the other half. This tapers the splice. (See Figs. 45 and 46.)
Q. How do you make a long splice?
A. Unlay the ends of two ropes to a distance three or four times greater than for a short splice, and place them within one another as for a short splice. Unlay one strand for a considerable distance and fill up the interval which it leaves with theopposite strand from the other rope. Twist the ends of these two together, then do the same with two more strands. The two remaining strands are twisted together in the place where they were first crossed. Open the two last-named strands, divide in two, take an overhand knot with the opposite halves, and lead the ends over the next strand and through the second as the whole strands were passed for the short splice. Cut off the other two halves. Do the same with the others that are placed together, dividing, knotting, and passing them in the same manner. Before cutting off any of the half-strands, the rope should be well gotten upon a stretch. Sometimes the whole strands are knotted, then divided, and the half-strands passed as above described. This splice does not increase the diameter of the rope, and it is used for splicing a fall or other rope that runs through blocks. (See Fig. 45.)
Q. What is a tackle?
A. A tackle is a purchase formed by reeving a rope through one or more blocks for the purpose of hoisting or pulling.
Q. Name the parts of a block.
A. The shell, sheave, pin, and strap. (See Fig. 49.)
Q. Describe the following blocks: Single, double, treble, snatch, and tail.
A. Single blocks have one sheave; double, two; treble, three. A tail-block is a single block strapped with an eye-splice and having a long end by which to make the block fast temporarily. A snatch-block is a single block having a notch in one cheek to receive the bight of a fall. (See Fig. 49.)
Q. What are the standing parts, the running parts, and the fall?
A. The standing parts are between the fasts and sheaves, the running parts between the sheaves, and the fall the part held in hauling.
Q. Describe the whip.
A. A rope through a single block. (See Fig. 49.)
Q. What is the power gained if the block be fixed?
A. None.
Fig. 49.
Fig. 49.
Fig. 49.
Q. Describe the whip upon whip.
A. The block of one whip is made fast to the fall of another. (See Fig. 49.)
Q. What is the power gained?
A. Double if only one block moves. Quadruple if both move.
Q. Describe the gun-tackle.
A. A rope passed through two single blocks and made fast to one. (See Fig. 49.)
Q. What is the power gained?
A. Double. Treble if block to which rope is made fast moves.
Q. Describe the luff-tackle.
A. A rope hove through a single and a double block and made fast to the single block. (See Fig. 49.)
Q. What is the power gained?
A. Treble. Quadruple if the block moves.
Q. What is a luff upon luff?
A. A luff-tackle on the fall of another luff. (See Fig. 49.)
Q. Describe the single Burton.
A. A rope rove through two single blocks, with a hook in the bight of the running part.
Q. What is the power gained?
A. Treble. Quadruple if both blocks move.
Q. How is power determined when one tackle is applied to the fall of another?
A. It is equal to the product of their respective powers.
Q. What is mousing, and what is its purpose?
A. A seizing around a hook to prevent it from spreading or unhooking. (See Fig. 49.)
Q. What is a bight of a hook?
A. The middle of a bend of a hook. (See Fig. 49.)
Q. Name the different parts of a garrison-gin.
A. It is composed of three poles (two legs and a pry-pole), braces, a bolt, clevis, windlass, two handspikes, three shoes, anda hoisting-apparatus consisting of two blocks (one triple and one double). (See Fig. 50.)
Q. How much can be safely lifted with it?
A. 17,000 lbs.
THE GARRISON GIN.Fig. 50.
THE GARRISON GIN.Fig. 50.
THE GARRISON GIN.
Fig. 50.
Q. How can the upper block be placed in position after the gin has been raised?
A. By rigging a truce rope through the clevis and hoisting it up.
Q. Explain briefly how you would raise a gin.
Q. Describe the parts of the shears.
A. Two spars lashed together at one point, forming an inverted V, the ends being called heels, the upper end the head, and the part where the lashing is applied is called the cross.
The equipment consists of the following stores: Two double blocks, two single blocks for gin-tackles; one double block, onetreble block, and one snatch-block for the main-tackle fall; guys, head-lashing, heel-lashing, and straps for main tackle; snatch-block, holdfasts, and some spun-yarn for mousing, etc.; two cleats for heels to prevent lashing from slipping; stakes for holdfasts for guys and heel-posts; two shoes for heels. (See Fig. 44.)
Q. What are shears used for?
A. For lifting heavy weights over the face of a wall or cliff, or in other situations where the gin could not be used for want of a footing for the pry-pole.
Q. How do you pass a shear-lashing?
A. Middle the lashing and take a turn around both legs at the cross; pass one end up and the other down, around and over the cross, until half of the lash is expended; then ride both ends back again on their own parts and knot them in the middle; frap the first and riding turns together on each side with sennit. This will be useful in rigging shears for hoisting guns when a gin is not available. Any two spars that will support the weight can be used. (See Fig. 51.)
Fig. 51.
Fig. 51.
Fig. 51.
Lay the middle of the back guy in the cross; bring the left-hand end up around the right leg and over the head of the left leg; then carry the right-hand end around under both legs; letit cross over the left-hand end, and seize them together with spun-yarn.
Q. How is a square lashing made?
A. Place two spars at right angles and pass several turns around two opposite angles of the X, then several turns around the other two opposite angles. Continue this until the spars are firmly lashed and will not move; tie the ends. This lashing is used to make two spars rigid and at right angles to each other.
Q. How are shears rigged and raised?
A. Lay the heads of the spars on a trestle about three feet high, the right leg above the left, so that they cross at about twice their thickness from the ends, with the heels in their proper positions.
Make a bowline-knot in the end of the fore guy and slip it over the head of both legs.
Lay the middle of the main-tackle strap under the cross above the fore guy; bring the ends up over the cross; hook the upper block to them under the cross below the fore guy and mouse it, taking care that the splice comes in the middle of the strap and that the fall leads to the rear.
Drive the heel-posts on each side the heels about a foot toward the head and one foot outside; lay the shoes under the heels; make a timber-hitch around the inner posts with the heel-lashings; pass three turns over the legs below the cleats, and hitch the lashings to the outer posts. Drive four holdfasts for each back guy, as follows: two on each side the line of the legs prolonged, three feet apart, and two six feet in the rear of these.
Lay the ends of the guy-straps over the front stakes; connect each pair of front and rear stakes with a strap twisted up taut to insure the strain being distributed properly.
Drive two holdfasts for the fore guy, one in the rear of the other, in the prolongation of the axis of the shears.
Hook the upper blocks of the guy-tackles to a bowline in the end of the guys, and the single block to the guy-strap, and mouse them all.
Ordinarily the fore guy can be worked without a tackle, belaying it over the holdfasts, first taking a round turn over the one next the shears. If not too heavy, the shears may be raised by lifting the head and hauling on the guy-tackles, slacking the heel-lashings as required, and tending the fore guy carefully to prevent the shears falling over toward the rear.
Q. How are shears held in position after being raised?
A. By guys and holdfasts.
Q. What is the inclination or rake of the shears with the level of the ground?
A. About 20 degrees.
Q. How can a change in the direction of the fall of the tackle be made to lead to a capstan?
A. Hook the snatch-block to a strap placed below the cleat on either, and pass the fall through it to the capstan.
Q. For what is the hydraulic jack used?
A. For lifting very heavy weights.
Q. What is the difference between the base jack and the horizontal jack?
A. The former has the lever, socket, etc., at the top of the jack, while the latter has the working parts near the base. (See Figs. 52 and 53.)
Q. What is the principle involved in hydraulic jacks?
A. A pump operated by hand forces a small amount of alcohol through a narrow valve into a recess containing a ram or large piston-rod. As the alcohol is forced into this recess it raises the ram: thus a weight upon the ram-head is raised. The alcohol is prevented from running back into the main reservoir by valves similar to those on all pumps.
Q. What is the best liquid to use in filling jacks?
A. For the base jack one part alcohol, two parts water; for the horizontal jack one part alcohol, one part water, and for both add a tablespoonful of sperm-oil.
Q. Name the principal parts of a jack.
A. The cylinder, ram, reservoir, socket, knuckle, piston, piston-valve, pump, pump-valve, lowering-valve, packing-springs, etc. (See Figs. 52 and 53.)
BASE JACK.Fig. 52.
BASE JACK.Fig. 52.
BASE JACK.
Fig. 52.
Q. How can a weight be raised when the jack will not go under the weight?
A. By the use of a movable claw.
Q. Give some general instructions for the care and use of the jack.
A. Never fill with water, kerosene, or wood-alcohol. Keep the ram down when not in use. If the valve sticks on its seat, strike the lever a few sharp blows up and down, thus jarring the valve. Use the alcohol supplied by the Ord. Dept.
HORIZONTAL JACKFig. 53.
HORIZONTAL JACKFig. 53.
HORIZONTAL JACK
Fig. 53.
Base jacks should never be used so that the head is lower than the foot. A jack should be used once a week to keep the packing in order.
Never apply more than 150 pounds to the lever: this equals about the weight of the average man.
Q. Point out the following parts of the Model 1903, Cal. 30 magazine rifle:
Barrel,Stock,Butt,Bayonet,Bolt,Trigger,Sights,Guard,Cut Off,Sleeve,Sleeve Lock,Stacking Swivel,Extractor,Ejector,Windage Screw,Firing Pin,Cocking Piece,Main Spring,Follower,Hand Guard,Drift Slide,Striker.
Barrel,Stock,Butt,Bayonet,Bolt,Trigger,Sights,Guard,Cut Off,Sleeve,Sleeve Lock,Stacking Swivel,Extractor,Ejector,Windage Screw,Firing Pin,Cocking Piece,Main Spring,Follower,Hand Guard,Drift Slide,Striker.
A. See Figs. 54, 55.
Q. Point out the following parts of the Ball Cartridge:
Case,Primer,Charge,Bullet.
A. See Fig. 56.
Q. What is meant by the term caliber?
A. It is the diameter of the bore in inches.
Q. What is the trigger pull?
A. Three to four and one half pounds.
Q. What is the weight of the rifle and bayonet?
A. 9·69 pounds.
Q. What is the maximum ordinate at 1000 yards?
A. 21·26 feet.
Q. What is the weight of the bullet?
A. 220 grains.
Q. What is the weight of charge of powder?
A. 42 grains of smokeless powder.
Q. What is the muzzle velocity?
A. 2200 f. s.
Q. How many cartridges will the magazine hold?
A. Five.
Fig. 54.U. S. MAGAZINE RIFLE, MODEL 1903.
Fig. 54.U. S. MAGAZINE RIFLE, MODEL 1903.
Fig. 54.
U. S. MAGAZINE RIFLE, MODEL 1903.
Fig. 55.U. S. MAGAZINE RIFLE, CALIBER 30, 1903.
Fig. 55.U. S. MAGAZINE RIFLE, CALIBER 30, 1903.
Fig. 55.
U. S. MAGAZINE RIFLE, CALIBER 30, 1903.
Fig. 56.CALIBER 30 BALL CARTRIDGE.
Fig. 56.CALIBER 30 BALL CARTRIDGE.
Fig. 56.
CALIBER 30 BALL CARTRIDGE.
Q. How is the rifle cleaned?
A. To clean the barrel, insert in the chamber a cartridge shell, the front end of which has been filled with a wooden plug, and close the bolt. Clean the bore with a rag saturated with soda water, or if this is not obtainable, with water. Wipe dry with clean rags. Remove the bolt and the cartridge shell, clean and dry the chamber from the rear. Thoroughly oil the chamber and the bore with a light coat of cosmoline oil. The stock and hand guard may be coated with raw linseed oil and polished by rubbing with the hand.
Q. When is the multiball cartridge used?
A. In cases where the great range of the service bullet would endanger persons or property at a considerable distance from firing.
Q. Of what is a multiball cartridge composed?
A. The service case charged with 34 grains of smokeless powder and two round balls.
Q. What is the effective range of the multiball cartridge?
A. 200 yds., when sights must be set for 350 yds. At 100 yds. or less fire point blank.
Q. Illustrate to the instructor how you would set the sight for a given range, using both open and peep sights.
Q. To shoot to the right (or left), which way would you move the sight?
Nomenclature.(For Reference Only.)COMPONENT PARTS.(One hundred and two in number.)
Barrel:Barrel. }Front Sight Stud. }Front Sight Stud-Pin. }Rear Sight Base. } Assembled.Rear Sight Base Pin. }Rear Sight Base. }Spline. }Bayonet:Bayonet Blade. }Bayonet Guard. } Assembled.Bayonet Guard Rivets (2). }Bayonet Catch.Bayonet Scabbard Catch.Bayonet Spring.Bayonet Spring Cup.Bayonet:Bayonet Grip, right. }Bayonet Grip Screw Washer. } Assembled.Bayonet Grip, left. }Bayonet Grip Screw Nut. } Assembled.Bayonet Grip Screw.Bolt:Bolt. }Extractor Collar. } Assembled.Bolt Stop:Bolt Stop Pin. }Bolt Stop Spring. } Assembled.Butt-plate:Butt-plate.Butt-plate Cap.Butt-plate Cap Pin.Butt-plate Cap Spring.Butt-plate Cap Spring Screw.Butt-plate Screw, large.Butt-plate Screw, small.Butt Swivel:Butt Swivel. }Butt Swivel Pin. } Assembled.Butt Swivel Plate. }Butt Swivel Plate Screws (2).Cut-off:Cut-off.Cut-off Spindle.Cut-off Spindle Screw.Cut-off Spring.Cut-off Spring Spindle.Ejector.Ejector Pin.Extractor.Firing Pin:Cocking Piece. }Firing Pin Rod. } Assembled.Firing Pin Sleeve.Follower.Front Sight:Front Sight.Front Sight Pin.Front Sight Movable Stud.Front Sight Movable Stud Screw.Floor Plate.Guard:Guard.Floor Plate Catch.Floor Plate Catch Pin.Floor Plate Catch Spring.Guard Screw, front.Guard Screw, rear.Guard Screw Bushing.Hand Guard.Lower Band.Lower Band Spring.Lower Band Swivel.Lower Band Swivel Screw.Magazine Spring.Mainspring.Rear Sight:Base Spring.Drift Slide. }Drift Slide Pin. } Assembled.Joint Pin.Leaf.Movable Base.Rear Sight:Slide.Slide Binding Screw.Slide Binding Screw Pin.Slide Cap.Slide Cap Screw.Windage Screw.Windage Screw Collar.Windage Screw Knob.Windage Screw Knob Pin.Windage Screw Spring.Receiver.Safety-lock:Safety-lock Spindle. }Safety-lock Spring. }Safety-lock Spring } Assembled.Spindle. }Safety-lock Thumbpiece. }Sear.Sear Joint Pin.Sear Spring.Sleeve:Sleeve.Sleeve Lock.Sleeve Lock Pin.Sleeve Lock Spring.Stacking Swivel.Stacking Swivel Screw.Stock.Striker.Trigger.Trigger Pin.Upper Band.Upper Band Screw.
APPENDAGES.
Cleaning Rod.Front Sight Cover.Oiler and Thong Case:Oiler and Thong Case, Collar,and Partition.Thong Case Cap and LeatherPad.Oiler Cap and Dropper.Oiler Cap Washer.Screw-driver.Thong and Brush:Brush.Thong Cord.Thong Tip.Thong Weight.
Q. What is an angle?
A. An angle is the divergence of two intersecting lines.
Fig. 57.
Fig. 57.
Fig. 57.
In Fig. 57 the two intersecting lines SA and XA form the angle SAX, and when measured on the circle with A as the center it is found to be equal to 80°.45 (eighty and forty-five hundredths degrees).
Q. Into how many degrees is a circle divided?
A. 360.
Q. How is each degree divided in the U. S. Artillery service?
A. Each degree is divided into one hundred equal parts.
Q. Define a circle.
A. A circle is a plane figure bounded by a curve, every point of which is equally distant from a point within called the center. Fig. 57 represents a circle withAas the center.
Q. What is the vertex of an angle?
A. The point where the two intersecting lines cross. As in Fig. 57,Ais the vertex of the angleSAX.
Q. Define an azimuth angle.
A. It is a horizontal angle measured from zero degrees at the south in a clockwise direction.
Q. What is meant by a horizontal angle?
A. One whose intersecting lines or sides are parallel with the level of water at that point.
Q. What is a vertical angle?
A. One whose sides lie in a plane of a plummet.
Q. Can an azimuth angle be greater than 90°?
A. Yes. See Fig. 51.SAT= azimuth of target (less than 90°);SAT'= azimuth of target (greater than 90°, but less than 180°);SAT''= azimuth of target (greater than 270°). (All these azimuth angles are read in aclockwise directionfrom zero at the south.)
Q. When is a gun or an instrument said to be set in azimuth?
A. When it reads zero and points south.
Q. What is an azimuth-instrument?
A. A device for measuring horizontal angles.
Q. Point out the following parts of the instrument:
1.Telescope-tube.2.Telescope-trunnion.3.Trunnion clamp-screws.4.Focusing-knob.5.Sunshade.6.Dew-cap.7.Objective-cell.8.Objective.9.Eyepiece-adapter.10.Eyepiece.11.Eye-lens.12.Field-lens.13.Cross-wire holders.14.Cross-wire.15.Brashear-Hastings erecting-prism.16.Prism-holder.17.Prism-cap.18.Cross-wire adjusting-screw.19.Instrument-base.20.Leveling-screws.21.Spindle-head.22.Worm-gear.23.Graduated circle.24.Worm-screw.25.Worm-box.26.Worm-box spring.27.Worm-box pivot.28.Worm-box adjusting-screws.29.Worm-box eccentric-crank.30.Index-disk.31.Index-pointer.32.Disk-crank.33.Worm adjusting-screw.34.Reading-opening.35.Azimuth-clamp.36.Azimuth slow-motion screw.37.Telescope-yoke.38.Yoke-caps.39.Levels.40.Level-holders.41.Level-adjusting screws.42.Plumb-bob.43.Plumb-bob chain.44.Tripod-head.45.Tripod-cap.46.Tripod-thumbscrew.47.Tripod-legs.48.Pier-mounts.
A. See Fig. 58.
Q. Describe how to set the azimuth-instrument up for use.
A. First: Set the graduated circle and index-disc to read the known azimuth of a visible object and clamp (the eccentric-crank being in gear).
Second: Set the eyepiece slightly to the left of the reading-opening and tighten the azimuth-clamp.
Third: Raise the whole instrument by grasping the tripod, and turn it so that the telescope points approximately in the direction of the visible object whose azimuth is known, being careful to set the plumb-bob over the home station at the same time and not destroy the setting of the graduated circle and index-disc.
Fourth: Level the instrument. (This is done by loosening the azimuth-clamp and setting one level parallel to two opposite leveling-screws, then turn these two screws eitherboth inwardtoward the spindle-head orboth outwarduntil the bubble comes in the middle. Perform the like operation with the other two leveling-screws and the instrument is level.)
Fifth: Release the azimuth-clamp and set the telescope as nearly as possible on the object, then clamp and set the vertical cross-hair exactly by turning the azimuth slow-motion screw. Verify the setting of the index-disc and the levels. The instrument is now set in azimuth. Azimuth instruments for mounting on the parapet have turned on their levelling screws so as to bring reading opening convenient to the eye.
Q. How is the azimuth of any other point read after the instrument is set up?
A. By turning the index-disc crank until the vertical hair cuts the object. Read the even degrees on the graduated circle, and hundredths of a degree on the index-disc. (In order to make a considerable change in azimuth-reading, much time is saved by releasing the eccentric-crank, turning the telescope approximately on the object, throwing the eccentric-gear again and readingaccurately by turning the index-disc till the vertical hair cuts the object.)
Q. Why arenotazimuth-circles on guns, mortars, etc., always graduated so that their zeros willpointsouth?