THE WAND.

The wand is a stick of light wood about 18 inches long and one-half inch in diameter. It is held loosely between the thumb and forefinger and waved rapidly to the right or left to indicate the elements of the alphabet. It is used for practice purposes and the signals made by it are only intended to be read at very short distances.

THE FLAG KIT.

Two kinds of flag kits, the 2-foot kit and the 4-foot kit, are issued by the Signal Corps.

The 2-foot kit.—This kit consists of one white and one red signal flag, two three-jointed staffs, and a suitable carrying case to contain the outfit. The white flag is made of white muslin 2 feet square, with an 8-inch turkey-red muslin center. The red flag is of similar size and material, the only difference being an alternation of colors in the body and center. The means of attachment to the staff consists of a loop at the center, and two ends of white tape at each edge, of the back of the flag body. The staff is made of hickory in three joints, each 23 inches long, and is assembled by telescoping into brass ferrules. Brass eyes are provided on the first and second joints to receive the tape ends at the edge of the flag. The carrying case, of convenient size and shape to contain the two flags and staffs complete, is made of 8-ounce standard khaki bound with leather and fitted with a shoulder strap.

The 2-foot kit is essentially a practice kit, although under favorable conditions of weather and terrain it may be used to advantage as a short distance service signaling outfit. Two of these kits are issued to each troop, battery, and company for the purpose of disseminating general instruction in military signaling throughout the army.

The 4-foot kit.—This kit is of essentially the same description as the 2-foot kit except as regards size. The flags are 3 feet 9 inches square with 12-inch centers and the staffs are considerably heavier, the joints being each 36 inches long. The 4-foot kit is the standard field flag kit and the range at which signals can be exchanged with it depends on a variety of factors, such as the condition of the weather, the location of stations, the proficiency of signalmen, etc. The speed for continuous signaling is seldom greater than five to six words per minute.

Care of flag material.—Signal flags should be examined at the close of drill or practice and repairs made to any rents or loose ties discovered. Flags, when soiled, should be thoroughly washed and dried in the sun. Signals made by clean flags are much more easily read than those made by dirty ones. Staffs should be handled with care, especially when jointing or unjointing. Care should be taken not to bruise the ends of the brass ferrules. If a ferrule becomes loose on a staff it should be tightened without delay.

Powers and limitations of flag signaling.—The advantages which may be claimed for this method of signaling are portability of apparatus, adaptability to varied weather conditions, and great rapidity of station establishment. The disadvantages are the lack of celerity of the signals, their impenetrability to dust or smoke, and the comparatively short ranges at which they can be read.

THE HELIOGRAPH.

The heliograph is an instrument designed for the purpose of transmitting signals by means of the sun's rays.

Historical.—Experiments with the heliograph with a view to its adoption as a part of the visual signaling equipment of the United States Army were commenced as early as 1878. The reported successful use of the instrument by the British in India about this time led to the importation of two heliographs of the Mance pattern. A series of experiments with these machines conducted for the purpose of eliminating certain objectionable features finally resulted in the evolution of the present type of service heliograph.

The early English heliograph was not provided with a shutter, the flash being directed on the distant station by means of a movable mirror controlled by a key. The great objection to this type of instrument was the impossibility of maintaining accurate adjustment during the transmission of signals due to the fact that the manipulation of the mirror tended to throw the flash constantly out of alignment. To overcome this, the American heliograph has been provided with a screen designed to operate as a shutter and control the flash reflected from an immobile mirror.

Description.—The service heliograph equipment of the Signal Corps consists of:

A sole-leather pouch with shoulder strap containing—

1 sun mirror.	}	Inclosed in a wooden box.
1 station mirror.
1 screen, 1 sighting rod, 1 screw-driver.

A small pouch, sliding by 2 loops upon the strap of the larger pouch, containing 1 mirror bar.

A skeleton leather case containing 2 tripods.

The mirrors are each 4½-inch squares of plate glass supported by sheet brass and cardboard backings, and mounted in brass retaining frames. At the center of each mirror there is an unsilvered spot three thirty-seconds of an inch in diameter and holes corresponding to these spots are drilled in the backing. The sun mirror differs from the station mirror only in that it has a paper disk pasted upon its face covering the unsilvered spot. The mirror frames are carried by brass supports provided at the bases with conical projections accurately turned to fit the sockets of the mirror bar and grooved at the ends to receive the clamping spring. Each support is fitted with a tangent screw and worm wheel attachment functioned to control the motion of the mirror frame about its horizontal axis.

The mirror bar is a bronze casting provided at the center with a clamp threaded to fit the screw of the tripod. By releasing the clamp the bar may be moved independently of the screw and adjusted to any desired position. Conical sockets for the reception of the mirror supports are provided at the ends of the mirror bar. These sockets work freely in the bar and, being actuated by a tangent screw and worm wheel, serve to regulate the motion of the mirror frame about its vertical axis. Clamp springs, for engaging and securing the ends of the mirror frame supports, are attached at each end of the bar.

The screen is a brass frame 6½ inches square, in which six segments or leaves are mounted in such a way as to form a shutter. The leaves are designed to turn through arcs of 90° on horizontal axes, unanimity of movement being secured by connections made with a common crank bar. The crank bar is operated by a key and retractile spring which serve to reveal and cut off the flash. A set screw and check nut at the lower edge of the screen frame limits the motion of the crank bar and the opening of the leaves. A threaded base support furnishes the means of attaching the screen frame to the tripod.

The sighting rod is a brass rod 6½ inches long, carrying at the upper end a front sight and a movable disk. About the rod is fitted a movable bronze collar, coned and grooved to take the socket and clamping spring of the mirror bar. A milled edged bronze washer serves to clamp the collar to the rod at any desired point.

The tripods are similar in all respects, the screw of either threading into the mirror bar or screen frame. Each tripod is provided with a hook at the base of the head, allowing the suspension of a weight when great stability is required.

Assembling.—There are two ways of assembling the heliograph and the position of the sun is the guide in determining which of the two should, in any given case, be employed. When the sun is in front of the operator (that is, in front of a plane through his position at right angles to the line joining the stations) the sun mirror only is required; with the sun in rear of this plane both mirrors should be used. With one mirror the rays of the sun are reflected directly from the sun mirror to the distant station; with two mirrors, the rays are reflected from the sun mirror to the station mirror, and thence to the distant station.

With one mirror: Firmly set one of the tripods upon the ground; attach the mirror bar to the tripod; insert and clamp in the sockets the sun mirror and sighting rod, the latter having the disk turned down. At a distance of about 6 inches, sight through the center of the unsilvered spot in the mirror and turn the mirror bar, raising or lowering the sighting rod until the center of the mirror, the extreme point of the sighting rod, and the distant station are accurately in line. Firmly clamp the mirror bar to the tripod, taking care not to disturb the alignment, and turn up the disk of the sighting rod. The mirror is then moved by means of the tangent screws until the "shadow spot" falls upon the paper disk in the sighting rod, after which the flash will be visible at the distant station. The "shadow spot" is readily found by holding a sheet of paper or the hand about 6 inches in front of the mirror, and should be constantly kept in view until located upon the disk. The screen is attached to a tripod and established close to, and in front of, the sighting disk, in such a way as to intercept the flash.

With two mirrors: Firmly set one of the tripods on the ground; clamp the mirror bar diagonally across the line of vision to the distant station; clamp the sun mirror facing the sun to one end of the mirror bar and the station mirror facing the distant station. Stooping down, the head near and in rear of the station mirror, turn the sun mirror by means of its tangent screws until the whole of the station mirror is seen reflected in the sun mirror and the unsilvered spot and the reflection of the paper disk accurately cover each other. Still looking into the sun mirror, adjust the station mirror by means of the tangent screws until the reflection of the distant station is brought exactly in line with the top of the reflection of the disk and the top of the unsilvered spot of the sun mirror; after this the station mirror must not be touched. Now step behind the sun mirror and adjust it by means of the tangent screws so that the "shadow spot" falls upon the center of the paper disk on the station mirror. The flash will then be visible at the distant station. The screen and its tripod are established as described in the single mirror assembling.

Alternate method with two mirrors: Clamp the mirror bar diagonally across the line of vision to the distant station, with the sun mirror and the station mirror approximately facing the sun and distant station, respectively.

Look through small hole in sun mirror and turn the station mirror on its vertical and horizontal axes until the paper disk on the station mirror accurately covers the distant station.

Standing behind sun mirror, turn it on its horizontal and vertical axes by means of the tangent screw attachments until the shadow spot falls upon the paper disk on station mirror.

Adjustment.—Perfect adjustment is maintained only by keeping the "shadow spot" uninterruptedly in the center of the paper disk, and as this "spot" continually changes its position with the apparent movement of the sun, one signalman should be in constant attendance on the tangent screws of the sun mirror. Movement imparted by these screws to the mirror does not disturb the alignment, as its center (the unsilvered spot) is at the intersection of the axes of revolution. Extra care bestowed upon preliminary adjustment is repaid by increased brilliancy of flash. With the alignment absolutely assured and the "shadow spot" at the center of the disk, the axis of the cone of reflected rays is coincident with the line of sight and the distant station receives the greatest intensity of light. Remember the distant observer is unquestionably the better judge as to the character of the flash received; and if therefore, adjustment is called for when the "shadow spot" is at the center of the disk, the alignment is probably at fault and should be looked after at once. In setting up the tripods always see that the legs have a sufficient spread to give a secure base and on yielding soil press firmly into the ground. Keep the head of the tripod as nearly level as possible and in high wind ballast by hanging a substantial weight to the hook. See that the screen completely obscures the flash; also that the flash passes entire when the screen is opened. This feature of the adjustment is partially regulated by the set screw attached to the screen frame. The retractile spring should sharply return all the leaves of the screen to their normal positions when the key is released. Failure to respond promptly is obviated by strengthening or replacing the spring.

Operation.—It is of the utmost importance that uniformity in mechanical movement of the screen be cultivated, as lack of rhythm in the signals of the sender entails "breaks" and delay on the part of the receiver. Dark backgrounds should, when practicable, be selected for heliograph stations, as the signals can be most easily distinguished against them.

To find a distant station, its position being unknown, reverse the catch holding the station mirror and with the hand turn the mirror very slowly at the horizon over the full azimuth distance in which the distant station may possibly lie. This should be repeated not less than twice, after which, within a reasonable time, there being no response, the mirror will be directed upon a point nearer the home station and the same process repeated. With care and intelligence it is quite probable that, a station being within range and watching for signals from a distant station with which it may be desired to exchange messages, this method will rarely fail to find the sought-for station.

The exact direction of either station searching for the other being unknown, that station which first perceives that it is being called will adjust its flash upon the distant station to enable it when this light is observed to make proper adjustments. If the position of each station is known to the other, the station first ready for signaling will direct a steady flash upon the distant station to enable the latter to see not only that the first station is ready for work, but to enable the distant station to adjust its flash upon the first station.

Smoked or colored glasses are issued for the purpose of relieving the strain on the eyes produced by reading heliograph signals.

Care of apparatus.—Minor parts of the instrument should be dismounted only to effect repairs, for which spare parts are furnished on requisition. Steel parts should be kept oiled and free from rust. Tangent screws and bearings should be frequently inspected for dust or grit. Mirrors should invariably be wiped clean before using. In case of accident to the sun mirror, the station mirror can be made available for substitution therefor by removing the paper disk. If the tripod legs become loose at the head joints, tighten the assembling screws with the screw-driver.

Powers and limitations of the heliograph.—Portability, great range, comparative rapidity of operation, and the invisibility of the signals except to observers located approximately on a right line joining the stations between which communication is had, are some of the advantages derived from using the heliograph in visual signaling.

The principal disadvantage results from the entire dependence of the instrument upon the presence of sunlight. The normal working range of the heliograph is about 30 miles, though instances of its having attained ranges many times greater than this are of record. The heliograph can be depended upon to transmit from five to twelve words per minute.

THE ACETYLENE LANTERN.

The signal lantern is an instrument designed for the purpose of transmitting signals by means of intermittent flashes of artificial light. It is the standard night visual signaling equipment furnished by the Signal Corps and depends for its illumination upon the combustion of acetylene gas.

Acetylene.—Acetylene is a pure hydrocarbon gas, producible in various ways, the commoner of which are: (a) By dropping calcium carbide into water; (b) by dropping water upon calcium carbide. This gas gives, when burning, high penetrative power, and was first described by Mr. Edmund Davy, professor of chemistry to the Royal Dublin Society, in 1836.

Calcium carbide.—In the manufacture of calcium carbide for commercial purposes the best quality of coke and quicklime are used. These two substances are powdered thoroughly, mixed in proper proportions, and then placed in an electrical furnace. Under the action of the intense heat (5,500° F.) these two refractory substances unite and form calcium carbide. Calcium carbide is of a grayish-white color, crystal in appearance, and is nonexplosive and noncombustible, being, except for its affinity for water, an absolutely inert substance. A pound of commercial carbide will produce approximately 5 cubic feet of gas. When water is brought in contact with calcium carbide, the generation of acetylene is rapid; owing to its strong affinity for water it will become air slacked and slowly lose its strength if exposed to the action of the moisture in the atmosphere; consequently, when stored or being transported it should be kept in air-tight cans.

When calcium carbide is brought in contact with water, the following occurs:

As is known, the principal components of water are oxygen and hydrogen, and calcium carbide is calcium and carbon. When brought in contact, the oxygen in the water decomposes the calcium in the carbide, and in this decomposition the hydrogen in the water is liberated and unites with the carbon of the carbide, forming a hydrocarbon gas which is acetylene. It is a pure white light of intense brilliancy and high candlepower. The spectrum analysis of acetylene shows that it is almost identical with sunlight, and in consequence delicate shades of color appear according to their true value as under the light of the sun, consequently it penetrates fog to a greater distance than other lights. Acetylene is like other gases—explosive when mixed with air in proper proportions, confined, and ignited—and the same precautions should therefore be taken in its use as would be in the handling of coal or water gas, gasoline vapor, etc. As acetylene is very rich in carbon, it will not burn in its pure state without smoking. To avoid this, burners have been constructed so that the gas is mixed with the proper proportion of air at the burner tip, to insure perfect combustion. The burners for acetylene are different from those for other gases. In order to get a flat flame, the gas is brought through two perfectly round holes at an angle which causes the two flames to impinge upon each other and thus form a flat flame.

Method of gas generation.—The method employed for producing acetylene in the signal lantern is by bringing water into contact with calcium carbide. The disadvantage of this method is that when the water is not in excess and does not entirely surround and touch each piece of carbide the heat of generation will so change the chemical properties of the gas that combustion at the burners is not satisfactory.

This change is technically known as "polymerization," or the breaking up of acetylene into other hydrocarbons, such as vapors of benzine, benzole, etc. These form a tarry substance which is apt to condense at the burner tip and clog the openings. Also they deposit carbon on the burners, as they require more air for perfect combustion than does pure acetylene. Another disadvantage of this system is that after the carbide and water are in contact, generation of gas will continue until all the water is absorbed. Where, however, portability of the generating apparatus is desired and resort to this method is necessary, the objections are not important, if the apparatus is well constructed and care is taken in its use.

Description.—This equipment consists of a signal lantern with cartridge generator attached. The lantern is equipped with a special aplanatic lens mirror, 5 inches in diameter and about 3 inches focus. The lantern is packed complete in a wooden case with shoulder straps and the following extra parts are included, each part having its own receptacle in the case: 2 burners; 1 cover glass; 3 cartridges of calcium carbide of 5 ounces each; 1 pair of gas pliers; 1 tube white lead; 1 extra filter bag; 1 screw-driver.

The lantern is made of brass, all parts of which are riveted. The burner is of the double tip form, consuming three-quarters of a cubic foot per hour. The lantern is fitted with a hood to provide proper ventilation and at the same time to prevent the flickering of the light by the wind. The front door of the lantern is hinged and fastens with a spring clasp; it is so arranged that it can be entirely removed if necessary. The cover glass is made in three sections and is not affected by the expansion and contraction of the metal due to changes in temperature. The glass is fastened by the aid of a spring wire, so that it can be readily removed if it is necessary to replace a broken section. In the base of the lantern is a key and the adjustment for regulating the height of the flame. The key is so arranged that when not depressed but little gas is admitted through the by-pass to the burner and the flame is low. By depressing the key as much gas as can be entirely consumed is admitted to the burner, which gives a bright flash. At the back of the lantern there is an adjustable handle, so that the equipment can be used as a hand lantern if desired. This form of lantern can be used with the regular heliograph tripod, the generator being either attached to the back of the lantern or suspended, as shown in figure 4. When practicable it is better to attach the generator to the lantern, as shown in figure 5. The candlepower of this lantern is about 1,900.

The generator used is known as "the cartridge generator," and while constructed on the water-feed principle, the disadvantages incident to this method are eliminated as far as possible. It is constructed of brass and has a removable top. Attached to the inside of the top is a flexible frame with a spring latch, the spring latch being hinged. (Fig. 8.) At the top of the frame is a tube or cylinder, the bottom of which is conical in shape and covered by a rubber plug. At the bottom of the frame is a hollow tube, which is the water inlet. The cartridge proper consists of a tin cylinder, having an opening at either end. A small cylinder of wire mesh extends from and connects these openings. The carbide lays around this mesh on the inside of the cartridge. The rubber plug before mentioned fits into the upper opening, and the water tube into the lower opening. (See figs. 7, 8, and 9.) Inside the tube, at the top of the frame, is a filter, the function of which is to remove the dust and moisture from the gas. The outlet from this chamber is by a brass bent tube having a stopcock attached thereto.

Figure 6 gives a sectional view of the generator with the cartridge in place. D F G H represent the valve frame and I the cartridge attached. The reservoir A is filled with water, and when the frame is immersed, with the valve R closed, the air contained in the cartridge and tubing can not escape, the water seal preventing, while the confined air prevents the water from rising in the tube N. When the valve at R is opened and the air is allowed to escape, part of the water from the reservoir rises into the tube N and then out through the small hole O to the carbide. Gas is immediately generated, the pressure of which prevents further ingress of the water from the tube N, and the generation of gas is suspended.

As the gas passes out through the valve at R the pressure decreases, permitting the water to again rise in the tube and flow through O. Gas is again generated, which at once exerts its pressure and cuts off the supply of water. This is the automatic action by which water is brought in contact with the calcium carbide. Thus it will be observed that the use or escape of the gas regulates the generation by the simple device of the rise and fall of a water column. There is a cap M screwed over the tube N. This is used to deflect the course of the water downward, so that the carbide in the lower part of the cartridge is first attacked. There is a needle inside of cap M, which can be used for cleaning the hole O. When the gas is generated it passes through the filter D on its way to the burner through R. This filter consists of a tube loosely packed with ordinary nonabsorbent cotton, which should never cover the escape pipe leading to the valve R. In passing through this cotton filter moisture and dust are removed from the gas. In the latest model a felt filter is used instead of cotton.

The escape pipe F provides a means for the escape of gas generated and not used or generated more rapidly than consumed. Should an excess be generated, it passes down through the tube F, and, finding its way through some small holes in the bottom of this tube, escapes through the water seal and the opening at C. It will be noted that if escaping gas at C should become accidentally lighted, the flame can not strike back into the filter and cartridge because of the water seal. The principal things to observe in the operation of this generator are the following:

(1) To see that the rubber plugs fit tightly into the openings of the cartridge.

(2) That the tube N, the cap M, and water hole O are not stopped up.

(3) That the cotton in the filter is changed frequently.

(4) That the stopcock R is closed before inserting the frame in the water. If this latter instruction is not complied with, it can be readily seen that the water will have free access to the carbide and excessive generation will occur.

When the charge is exhausted, the entire cartridge is taken out and thrown away. This eliminates the handling of carbide and the disagreeable task of cleaning out the residuum after the gas has been extracted.

Connection is made from the stopcock R to the hose connection on the lantern proper, and this is the passageway of the gas from the generator to the burner. As soon as the stopcock is opened the water rises through the tube and flows to the carbide. The advantage of the cartridge being submerged in the water is to reduce and absorb as much of the heat liberated by generation as is possible. These lanterns have been tested up to a distance of 10 miles with the naked eye, and under favorable conditions can be used over a range somewhat in excess of this. With a 30-power telescope the flash can be read at a distance of 30 miles.

Operation and care.—Take the lamp and generator from the case by aid of the handle attached to the lamp; screw the complete outfit on a heliograph tripod, or stand the outfit on a level object; remove the cover of generator, to which is attached the flexible frame (fig. 9); detach spring from the catch of the flexible frame; tear off flaps from the ends of carbide cartridge (or pry off small caps) and attach the cartridge as shown in figure 9. Then attach to frame as shown in figure 10, being careful to see that both rubber plugs fit tightly into the holes in the cartridge; fasten the latch of the spring over the metal catch; close stopcock R on service pipe; completely fill the outer can of generator with water, the object being to have the generator level full of water when the lamp is in service, then immerse the frame and cartridge, pressing the top of the generator down tight. In doing this the water will overflow the sides of the generator tank. Now connect by rubber tubing the stopcock with the gas inlet at the bottom of the lamps, as shown in figure 4; then (1) open front door of the lamp, (2) light a match, (3) open stopcock, and (4) light the gas at the burner. In doing this hold the key open. In the new model the key and hose connection are on the side of bottom of lamp.

When the gas is ignited, the lamp is ready for signaling, and the key can be operated as is the Morse telegraph instrument, but of course not so rapidly.

In the event of the flame being too high when the key is closed, adjustment can be made by loosening the set screw (fig. 4, indicated by an arrow) and adjusting the light by turning screw b. When at the proper height, tighten the set screw which locks the by-pass in its proper position. In the new model this is accomplished by aid of the regulator by-pass valve at the left-hand side of bottom of lamp. The lamp is properly adjusted when shipped and should not be changed unless absolutely necessary. Connect the rubber tube to the burner before opening the stopcock on the generator.

To recharge the generator, take the frame and the old cartridge from the case, throw away the old case and replace with a fresh one, proceeding as before. See that fresh water is put in the generator each time a new cartridge is used.

In the tube through which the service pipe passes is a felt filter for taking the dust out of the gas. If the filter clogs, unscrew the cap to which the service pipe is attached, clean the felt, or replace it with a new filter, binding it in place by a stout thread or string.

If the burner of the lamp does not produce a perfectly flat flame it has become clogged and should be cleaned with the burner cleaner furnished, or a new burner should be substituted, care being taken to put a little white lead on the nipple, if practicable, so as to insure a tight joint.

In repacking the outfit in the case, throw out the water and wipe the can and generator parts dry. You can not be too careful to keep the apparatus clean. This is especially true of the small pipe that passes up through the bottom of the cartridge, with a cap over it. The cap should always be screwed in place, as its object is to prevent the water from squirting to the top of the cartridge.

The back of the lamp can be removed by turning the small thumbscrew on the top and drawing out the pin which holds the shell into which is fitted the lens. It is not necessary to take the back out except to replace a lens, as the latter can be cleaned by opening the front door.

If it is desirable to use the lamp as a hand lantern the flame can be turned on full by turning the button in a vertical position; this locks the key open. In the new model depress the key and lock it with the latch above the key.

One charge of calcium carbide will supply gas to burn about one hour with the light turned on full, or for approximately three hours' signaling.

If signaling is to be suspended for some hours, empty the water out of the generator and close valve R.

The glass front can be replaced by taking out the wire spring. The glass cuts should be mounted in a horizontal position and, to prevent breaking, should be protected from rain when the lamp is hot. If a glass should be broken and an extra one is not available to replace it, signaling can be continued by turning the flame on full and using the heliograph shutter, a cap or piece of board in front of the lantern to obscure and reveal the flash. Without the protection of the cover the flame is easily blown out when turned low, but will not be extinguished even in a strong wind if the gas is turned full on.

Old model lamps are serially numbered from 1 to 200, inclusive; the new model lamps are serially numbered from 201 upward.

Powers and limitations of the acetylene signal lantern.—As conditions are usually more uniform at night than in the daytime, the signal lantern is probably the most reliable of all visual signaling outfits. The advantages of this form of apparatus are its portability, speed of operation, and comparatively great range. The principal disadvantages are due to the interference caused by rain, fog, and moonlight. The speed attainable with the lantern is about the same as that attainable with the heliograph.

ROCKETS AND SHELLS.

Two distinct kinds of rockets and shells are issued, one of which is adapted to day and the other to night signaling. Shells and rockets of the amber smoke type with parachutes are used in the daytime, while shells (red and white) and sequence rockets are used at night.

Description.—The shells are all single shot and are fired from a 5-inch portable mortar, attaining a height of about 550 feet. The report of explosion can be heard at varying distances up to 5 miles, depending on weather conditions. The parachute attached to the smoke shell suspends a small light wooden tube[36]
[37]
[38] which, after ignition, emits smoke for from four to six seconds. The red and white shells, on bursting, discharge a shower of red and white fire which can be observed for some time, in fact almost until the sparks fall to the ground.

Rockets for both day and night signaling are equipped with parachutes. The smoke rocket is of similar construction to the smoke shell. The sequence rocket is so arranged at the base that threaded sections of combustible material burning either red or white can be attached to it. Rockets ascend about 700 feet.

Each rocket and shell is supplied in a cylindrical sealed tin can, which also contains a port fire, wind matches, and for the rockets a stick in four sections. On the outside of the can is a label designating the kind of shell or rocket therein contained. These cans are easily opened by pulling a ring and require no special opening tool.

Operation.—In firing shells the mortar should be surrounded by earth or sand, preferably placed in sacks. The fuse for all shells is very rapid and should be ignited by attaching the port fire to a long stick.

All of the old type Signal Corps mortars, originally designed to withstand a pressure of 1,000 pounds per square inch, and made of ordinary iron pipe, are considered unsafe and should be immediately destroyed. The new mortars, recently made for the Signal Corps by the Ordnance Department, are of cold-drawn steel having a tensile strength of 6,000 pounds per square inch, which is more than the maximum pressure for firing any of the Signal Corps bombs. They are stamped "Signal Corps, U. S. A., Model 1907," or "Rocket Gun, Watertown Arsenal, 1907."

The sequence rocket is prepared for use by attaching red or white sections to the base in such a combination as to form letters of the alphabet which it is desired to use. Letters containing the same color in sequence are very difficult to read and should be avoided whenever possible. If necessary to use them, blank sections furnished for the purpose should be inserted between the units. The base of the rocket will secure six units.

When rockets are to be fired the sticks must be firmly attached, the rocket placed upright in a trough, upon a frame, or against a post. If the fuse is beneath the paper covering the "choke" orifice, the paper should be torn off and the rocket ignited by a port fire. In the rockets now used the fuse extends through the covering and can be lighted direct. If the night be damp this fuse should be exposed only a moment before the rocket is fired. If several rockets are to be fired in succession it is well to prepare them all at the same time, and to have them all stood upright, but each separated from the other at a distance of at least 6 feet, else one may ignite the other accidentally. In firing for chronosemic signals, one rocket ought to be kept ready upon the frame and in reserve, to be fired in place of one that fails.

If a rocket misses fire it is to be taken from the stand and laid on the ground. Its place is at once supplied by a similar rocket, fired in its stead. The failing rocket is laid on the ground pointed away from the station in order that if it has only hung fire and should afterwards ignite it may not disarrange the signal shown or injure any one of the party. If the wind blows freshly the rocket to be fired should be inclined slightly against the wind.

Signal rockets and shells are furnished in sealed cans and should not be removed therefrom until ready for use. Strict economy should be observed in the use of these articles and on no account should they be used for purposes of display.

Employment.—Rockets and shells are especially valuable in making preconcerted or emergency signals. On account of the great amount of ammunition required it is impracticable to spell out messages with them. These articles should be supplied to outposts, detached stations, etc., to be used for signaling the approach of the enemy or the happening of unexpected events, the necessity for promptly knowing which is important.

THE SEMAPHORE.

If signal stations are to be permanently occupied, and it is impracticable to electrically connect them, communication may be facilitated by erecting semaphores.

Semaphores, while primarily used for day signaling, can be advantageously used at night by attaching lights to the arms.

The navy semaphore consists of four arms pivoted at the ends, three on one side of the upright, or pole, and one on the other side. These arms have three positions: Horizontal; upward at an angle of 45° to the horizontal; downward at an angle of 45° to the horizontal.

Full instructions for the operation of the semaphore, and also for the use of balls, cones, drums, pennants, and whefts as distant signals, are given in the International Code of Signals.

THE SEARCHLIGHT.

The electric searchlight, when available, can often be successfully employed for night signaling, frequently affording efficient means of communication between ships and shore stations, when wireless working is impracticable. This system of visual signaling is practicable and especially valuable where the stations are, on account of the terrain, not intervisible.

Methods of employment.—In signaling with the searchlight the usual method of handling the shaft or beam is identical with that employed with the flag. In the first position the beam is shown vertically, while motions to the right, the left, and directly serve to indicate the elements of the alphabet. Chronosemic signals may also be used in searchlight signaling, the shaft of light being directed intermittently on some conspicuous object, such as a cloud, balloon, or high mountain top.

COSTON SIGNALS.

These signals are pyrotechnic compositions which burn with great intensity of light and color. The colors red, white, and green are found best suited for signaling. The signals are prepared in the form of cartridges and are burned from a holder. The colors burned may indicate the elements of any alphabet, or such other special signals as may be desired.

VERY'S NIGHT SIGNALS.

The Very system employs projected red, white, and green stars, which are shot from pistols held in the hand.

Description.—The Very pistol is a breechloading, single-shot pistol with an 8-inch steel barrel chambered to receive a 12-gauge commercial shotgun shell. Brass shells are used and are packed in boxes colored to indicate the character of stars employed in loading. The color of the star fired may indicate an element of any alphabet or any special signal which may be desired. The stars rise to a height of about 200 feet and remain visible for some time.

THE ARDOIS SYSTEM.

The Ardois system is a special system of night signaling designed to utilize combinations of red and white signal lights in forming the elements of any desired alphabet. Four signal lamps capable of displaying either red or white lights are attached at convenient intervals to a vertical cable or staff rigged between the top of a mast and the deck, if on shipboard, or the ground, if on shore. Illumination is furnished by electrical means and any desired combination of lights is automatically obtainable by operating a keyboard.

This system is valuable on vessels or at permanent shore stations, but the great expense of installation precludes its general use. Wiring diagrams and technical instructions relative to this apparatus are in all cases furnished when the same is issued.

SOUND SIGNALS.

When recourse to any method of sight signals can not be had on account of weather conditions or lack of suitable apparatus, sound signals may often be advantageously used. The commoner means of furnishing sound signals are the horn and the whistle, though many other kinds of apparatus are practicable. The necessary elements of any system can be indicated by one short, two shorts, and a long blast. The advantage of this system of signaling is that it can be used in any kind of weather, both in daytime and at night. On the other hand, sound signals are generally more difficult to read than sight signals and tend to disclose the presence of stations to hostile forces.

IMPROVISED SIGNALING METHODS.

The object of this chapter has been to describe only the standard visual signaling equipment issued and generally utilized. Besides the methods detailed, there are many others which may be successfully employed by the ingenious signalman when the necessity for them arise. The use of any means of transmitting signals whatever is justifiable when for any reason the regular apparatus is not available. Special conventional scout signals are given in paragraph 82, Field Service Regulations.

In the field many instances will occur where it will be necessary to transmit information rapidly without recourse to the authorized equipment. This will be especially true of outposts, detached stations, patrols, and other small bodies of troops, and it will devolve upon individual commanders to improvise methods of signaling best suited to the occasion and the conveniences at hand.