United States. Army. Signal Corps

“ When a signal station is to communicate with two or more stations, a telescope should be firmly fixed bearing on each, when practicable, and so far apart that those communicating with one station will not disturb the other party. ”

“ Having chosen a point entirely in view of the station or stations to be communicated with, and having fixed the exact position of the signaling apparatus, the color of the background should be determined as carefully as conditions of terrain will permit. If the elevation of the distant station is without doubt greater than that of the home station it is safe to assume that the color of the background will be that of the objects directly around and behind it. On the other hand, if the distant station unquestionably occupies the lower position, a sky exposure will usually result. ”

“ To find a signalman near any known station, note with the unaided eye some prominent landmark near which the looked-for person or object is supposed to be, and direct the telescope upon the place, as sight is taken over a gun barrel, covering the object; if the eye is now placed at the eyeglass of the telescope, the prominent or directing landmark will be found in the field of view. ”

“ In most systems of signals suitable for military use, each signal is composed of one or more separate units, known as elements. Having prescribed a certain number of elements, the various signals are formed by having these elements appear singly or together in different arrangements or combinations. The continental system is one of two elements, namely the dot and the dash, while the Morse system employs three elements, the dot, the dash, and the space. Having agreed upon a certain number of combinations of elements, a system of signals is formed by giving a meaning to each combination. ”

“ The power of a telescope or a field glass can more accurately be measured by means of a dynameter, which is a microscope which can be fitted over the eyepiece end of the instrument, and which magnifies the image. ”

“ The telescope is an optical instrument based on an object glass or reflector to form a real image of a real and distant object, and of an ocular to magnify and view the image. Telescopes are classified as refracting or reflecting according as the object glass is a lens or a reflector. The object glass must be essentially convex if the telescope is a refractor, and if a reflector, the object mirror must be concave ”

“ 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. ”

“ 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 ”

“ The assignment of men should be such that a continuous watch for signals is kept and the responsibility for neglect to promptly answer calls determined. Of the station men, one is the sender, whose duty it is to transmit all signals to contiguous stations. Another, the receiver, attends the telescope and reads and calls off the signals displayed at the distant station. A third man acts as recorder, alternately calling off the outgoing message to the sender or transcribing the incoming message repeated by the receiver. ”

“ Field glasses with low magnifying power, which are usually preferred by ordinary observers, have their chief value in the comparatively extensive field of view; they should be used to observe extensive movements, where large tracts of country must be taken in one field of view or in sweeping the landscape to find the tents of the enemy, their wagons, etc., or other objects, to be afterwards more closely examined with the telescope. ”

“ When light falls on a transparent body, part is reflected and part is refracted. The angle which the ray makes with the normal, or perpendicular, to the surface at the point of contact is known as the angle of incidence, and the angles which the reflected and refracted rays make with the same normal are known respectively as the angle of reflection and refraction. ”

“ It is time gained to do so; it is a loss of time and an annoyance to run letters together. Nothing so distinguishes the good from the indifferent operator, visual or telegraph, as this. When signals are being made with a flag, a fraction of a second will be ample. In using the lantern or heliograph, the pause between letters should be relative to the time of display of the elements, longer than with the flag. To prevent any entangling of the flag upon its staff, skillful handling, acquired by practice, is necessary. ”

“ A high-power glass is unsuitable for use at night, hazy atmosphere, or for use of a mounted man where the glass can not be rested against a firm support. A low-power glass with large object lens to permit as much light as possible is a necessary condition for use at night. ”

“ The Chief Signal Officer of the Army reserves the right to inspect any or all processes of manufacture, and unsatisfactory material will be marked for rejection by the inspector before, during, or after assembly, as occasion may arise.
Each glass will be tested for power, field, definition, and light. Any glass which is not the equal of the sample and model in all respects will be rejected. ”

“ Visual signaling is and always will be a most valuable means of transmitting information [10] in peace and war, and it is not to be imagined that it will ever be supplanted in its particular function by the introduction of other methods. Occasions will frequently occur in the field when no other means will be practicable, and then, if not before, will the value of the system be fully emphasized. ”

“ The rays of light emerging from the ocular of the Galilean telescope are divergent and cover an area much greater than the size of the pupil of the eye. As all rays falling outside the pupil of the eye are lost, but a small field of view can be seen, as in looking through [108] an ordinary cone from the larger end. The prism glasses are constructed on the opposite principle. The rays of light gathered by the objective emerge from the eyepiece in a converging pencil of light small enough to enter the pupil of the eye, thus giving a larger field of view ”

“ Dark backgrounds are far more common and more easily obtainable than sky exposures. They afford the maximum means of concealment from hostile observation, but materially reduce the range, speed, and accuracy of signal transmission. ”

“ No advice or fixed rule can be stated as to what constitutes the most suitable characteristics of a field glass. No single field glass can furnish maximum results under all conditions on account of varying conditions of the atmosphere. ”

“ Strictly speaking, a visual signal is any visible sign by which intelligence is communicated, but in a military sense the term visual signaling has a broader meaning and includes other methods of transmitting information than those which appeal to the sense of sight. ”

“ 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 correct determination of background color from the vicinity of home stations is usually difficult and unsatisfactory, and it is considered the best method to establish communication with the distant station by simultaneously using several kinds of signaling apparatus, that kind producing the most intelligible signals being retained for continued use. ”

“ When the general direction only of the object can be given and it is sought for, the whole landscape in that direction to the horizon should be divided into sections by imaginary lines, the limits of these sections being bounded between visible landmarks through which the bounding lines are supposed to pass. Each section should be scrutinized little by little until the glass has been passed over every spot. Such search will seldom fail to be successful. ”

“ Signal stations should be convenient for messenger service and hence as near commonly traveled roads as the physical contour of the country will permit. Locations for signal stations should be so selected that the visual lines do not cross traveled roads, camps, etc., as dust and smoke in the daytime and lights at night are factors in determining the visibility of signals. Signal stations can if necessary be artificially concealed by erecting screens constructed of limbs of trees, etc., about the flanks and rear. Sheltered positions should be utilized in windy weather. ”

“ Each and every operator will also have a personal signal of like character. Station calls or personal signals when once given or assumed will not be changed except by order of higher authority. Every station should at all times have on hand a list of all calls and personal signals liable to be encountered in station working. The general call suited to attract the attention of any station whose regular call is unknown [79] will always be a signal represented by the letter "A" in the Morse or the letter "E" of the Army and Navy Code. ”

“ 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, [35] 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. ”

“ 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. ”

“ 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. ”

“ Definition.—The term "field message" is applied to all messages sent over field lines of information. All field messages for transmission over field lines of information by electrical or visual means should be plainly written by the sender on the blank forms in the United States Army Field Message Book. The practice of verbally delivering telegrams to enlisted men for transmission should invariably be discouraged. ”

“ Focus on printed matter at a distance just beyond that at which perfect clearness is given and gradually approach until the letters are distinctly defined. The instrument with which the print can be read at the greatest distance has the best definition. ”

“ 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. ”

“ 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 [40] 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. ”

“ A hostile command 10 miles distant could be seen theoretically as well as if they were only 53 feet away, and the slightest movement of each single man would become visible. Of course no such wonderful effect is physically practicable, and the limiting conditions increase greatly in proportion as either one or the other of the qualities, power, field, etc., is especially sought. ”

“ 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. ”