The Science Notebook
Gilbert Signal Engineering - Part 1

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NOTE:  This book was published in 1920, and while many of the experiments and activities here may be safely done as written, a few of them may not be considered particularly safe today.  If you try anything here, please understand that you do so at your own risk.  See our Terms of Use.   

NOTE # 2:  Some of the codes in this book have changed slightly.  For example, the International Morse Code, known at the time as the "General Service Code is still used today and is as shown in this book.  (See p. 15.)  However, some of the "conventional signals" have changed.  (See p 17.)  Learning to send or receive Morse code by sound, light or semaphore might be a little hard, but it can be a lot of fun, but before you attempt to learn it, be sure you are using the correct code and signals for today.  You should be able to get the current version of the code or sending method you want to use online.  Check out our Downloads and Useful Links pages for additional information.

Cover - page 25


Complete and thorough instructions in all forms of Signaling


Formerly with Signal Corps U. S. Navy Prepared under the Direction of
Yale University, 1909


New York     Chicago     San Francisco    Toronto     London





Wigwag system - The flag, limitations and backgrounds - The torch and lantern wigwag - Wigwagging by searchlight.

The message - Duties of a signal unit - Interruption of messages - Intervals - Code time.

The semaphore machine - Two-arm semaphore by hand flags.

Sound signals by bugle - Signaling by pocket whistle - Flashing or occulting light system - The blinker - The acetylene lantern - Searchlight signaling - The heliograph - The Ardois system - The Very system.

Telegraphy - The American Morse Code Receiving telegraphy - Radio-telegraphy Telephony - The telephone for signal purposes.

Suggestions for erecting a signal tower - Secret codes and ciphers - The cipher disc - How to make a cipher outfit.

Flags and correct way of using - Flags of the International Code and how used - Method of signaling when no other ships are in sight - Distant signals - International flag waving system.

How navy signals are executed - Calls - U. S. naval flag etiquette - Time for flying colors - Personal flags - Yacht flags.
International life saving signals - Signals for a pilot - International distress signals, for day - International distress signals, for night.

How to make a field buzzer - How to make a heliograph - How to make a semaphore and blinker.


To do big things, just as men do who are experts in a certain kind of endeavor, I believe is the greatest wish of every boy. I know when I was a boy it was very interesting to me to find out all I could about electricity, chemistry and other practical subjects because they held my attention. There was all kinds of fun in this for me. Whenever I got working on my experiments I had the greatest amount of pleasure. Let me tell you, too, I was a happy boy when I had completed my work and could show it to others.

I remember how I used to watch army men at signal practice. It was mighty fascinating to see them at the camp with their apparatus and to observe the methods they used to send messages. It looked hard, but when I thought it over it seemed very easy.

Signaling will prove just as interesting to you as it did to me, and because I think it means a great amount of fun for you, I have had this book prepared by a man who was an expert in signals and who did very fine work in the Navy as a member of the Signal Corps. Every detail is explained with the greatest care. The facts are authentic and you can depend on this book to give you a thorough knowledge of signaling. You can learn about signals from the very beginning when firebrands were used in a primitive fashion many years ago to the present time when messages are flashed and sent by the most modern inventions.



FIG. 1
Competing teams of the U. S. Army and Navy on the roof of the Grand Central Palace, New York City, during a recent signal contest.

Chapter I

In Webster's Dictionary we find that the meaning for signal is a sign and in looking up sign find its definition to be signaling hence they are certainly very closely related. At any rate a signalman is one who puts signs into action and that is what we are going to do, By a little perseverance you will master


each lesson step by step and in a very short time, with the ease of a master signalman, be able to flash a message through space for a distance of twenty miles or more.

The early American Indians wrote their picturegraph messages on the bark of trees, their canvas wigwams and other conspicuous places. The totem pole of the Northwest and Alaskan Indians is a good example of symbol writing. In later years the more advanced tribes devised crude codes by which they sent messages by means of smoke.

Many hundreds of years ago the ancient tribes in Europe put into practice the habit of carving picturegraph stories on rocks. Like the American Indians, they later found methods of sending their messages through Space with the aid of a cumbersome code and lighted torches.

FIG. 2
Boy Scouts in mountain of N. Y. State signaling from a platform erected in a tree.
Courtesy  of Boy Scouts of America.

It seems that the earliest forms of optical telegraphy, as visual signaling is sometimes called, involved the use of firebrands or torches. Of course these could only be used at night and , and his-


FIG. 3  
Boys practicing signals at a Scout Camp.
Courtesy of Boy Scouts of America

FIG. 4  
Boy Scouts of a Denver, Colo., Troop practicing semaphore.
Courtesy of Boy Scouts of America


tory gives us no reliable records of any day signals until the earlier forms of semaphore hundreds of years later.

About 200 B. C. a method of signaling was employed by the Greeks, in which torches were used. A system of measuring the flashes or exposures so as to make a simple code was invented.

The Romans also used torches for signaling, and during the early Greek and Roman Wars probably the first step was taken in Signal Corps organization. These warrior signalmen were known as "fire shakers," and to obtain points of vantage they built in many places throughout Europe signal stations, some of which are still standing to this day.

Mention is made in the Old Testament of lighting signal fires for the purpose of conveying intelligence. It seems that the method of using signal fires and torches was very popular among the early signalmen. The fact remains that even as late as the Civil War in America torches were still in use by the Signal Corps of the Blue and Gray Armies and are rivaled today only by the more modern devices in which lanterns and electric lights are used.

In the year 1623 the Marquis of Worcester (England), invented a plan of letters for signaling by day and night.

Monsieur Amontons (France 1663) recommended the holding up of large letters of the alphabet to be viewed by telescope.

Robert Hook of England was the first to really develop the modern idea of visual signaling. He used various shaped objects, suspended on a frame, to indicate letters of the alphabet.

Claude Chappe, a young French engineer, in 1790 invented a system of semaphore, and other Frenchmen followed him with the more advanced forms of indicators with semaphoric wings.

During the reign of Queen Elizabeth, the Duke of York (later James II) introduced a system of methodized signals from which later sprang the first British Naval Code.


FIG. 5
Signalmen of the U. S. Navy on signal bridge of the U. S. "Wyoming"


In 1816 Sir Home Popham of the British Navy gave the world a new system of semaphore telegraph, which was adopted by the British Admiralty.

William Penn of America is also given credit for being among the first (if not the first) to get together a code and system for communication at sea.

In reviewing the history of signaling it might be of interest to know that the first telescope was invented about the year 1600. This important invention increased the range of the naked eye to a very great extent and made signaling an important method of communication.

The needs for signaling, we can see, were first wanted by armies so as to bring about rapid exchange of thoughts. It proved faster and more reliable than messengers, who were always subject to delays or liable to capture. Still, today, its paramount use is found in the armies and navies of the world, where the Signal Corps is without a doubt the most important branch.

In November, 1863, during the Civil War in America, when General Grant took command of the Union Army before Chattanooga he established his Signal Corps on a big mountain and was able to keep in touch with his forces during many of the great battles, one of which was the famous "Battle Above the Clouds" fought on Lookout Mountain. Today this mountain, from which his Signal Corps operated, is called Signal Mountain and will stand as an everlasting monument to the Signal Corps. If it is ever your good luck to visit this beautiful spot in Tennessee you will then realize to what extent accurate signals were and can be exchanged.

During the late war the Allied armies used many ingenious methods of signaling, including the improved blinker systems, sound systems and radio. One of the newest schemes is that of sending a message from the ground to aeroplanes by means of


"Panels." This is done with a code and panels of colored cloth laid on the ground.

The importance of Signal Corps work can be realized better when it is known that the Signal Corps of the U. S. Army alone, during the time it took part in the war, used 126,000 miles of wire for intelligence communications by telephone and telegraph lines. (Liaison work.)

More scientific knowledge of our neighboring planets will undoubtedly be accomplished by means of high powered signal apparatus. The matter of an exchange of messages with the inhabitants (if any) of these planets is receiving serious thought by many scientists. Several years ago a plan was advanced to do this by means of the heliograph method. This scheme was to use great mirrors with a huge shutter arrangement so as to send the messages by means of great flashes. Who can tell but what you may be able to invent the apparatus to send a message that far? It would, of course, take years to develop, but some one will eventually find a way to complete this wonder system in signaling.


Chapter II

A code of signals is a collection of symbols agreed upon. The International Morse or Continental Code is the most widely used of all modern codes due to its easy adaptability to so many forms of signaling.

The International Morse Code was first used for transmitting messages by ocean cables and later adopted by the armies and navies of the United States and Great Britain. By the official recognition of the Army and Navy, the Boy Scouts and other organizations it has come to be known as the "General Service Code." From this point on in the book it will be called by that term.

The General Service Code is a code of dots and dashes comprising the twenty-six letters of the alphabet and the numerals, with additional symbols.

The following signal systems are based on this code:

1. Sound system.
2. Heliograph system.
3. The Ardois system.
4. Flashing or occulting light system.
5. Very's night system.
6. The Wigwag system.
7. Radio.
8. Buzzer and Field Telegraph.

The U. S. Army, commercial telegraph lines and short cables at the present time use the American Morse which has slightly different symbols.




In using the General Service Code with some of the systems just mentioned, it is necessary at times to make some minor changes in the arrangement of sending numerals and conventional signals, but the principle of the code always remains the same. The changes will be explained from time to time as you become familiar with the systems.

You can readily see the importance of knowing this code before any advance can be made in signaling; so now turn to Chart 1 where you will find the General Service Code alphabet and numerals written.

First study the alphabet. A good plan that will help you to  memorize it will be to write over and over again the characters on paper, after which you can get another boy to test your  memory by having him call out at random letters of the alphabet to you. You can reply in dots and dashes. Another way is to construct short sentences and then rewrite them under the dot  and dash characters. For example;

The numerals of the code are much easier to learn than the alphabet. You will note that they are written by using a combination of five dots and dashes for each number. Remember numbers are always represented by five dots, dashes, or a combination of both. Number one is made with one dot followed by four dashes,  . - - - - ; number two by adding






another dot and dropping one dash, . . - - -. This same plan is followed until you reach number six, when you start with one dash followed by four dots - . . . For number seven write two dashes and drop one of the dots,  - - . . . , and so on down the line to zero which is expressed by five dashes - - - - -

Chart 2 gives the punctuation marks of the code, secondary meanings of several letters of code alphabet, conventional signals and abbreviations, most of which were taken originally from the American Morse Code but are adaptable to all methods of signaling and are used by every practical signalist.

In using abbreviations, no matter what the system, always remember they are sent as a complete word.


Now that you know the General Service Code, you are ready to make use of this knowledge by practicing short messages with the Wigwag System.

In the Army, for practicing the wigwag, a stick of light wood about 18 inches long is used, and is called the wand. The wand is held loosely between the thumb and forefinger and waved rapidly to right or left to indicate letters of the code. A wand can be made easily from the small end of a bamboo pole or any
light wood.

By referring to Chart 3 you will see illustrated a boy holding the single stick flag at position or ready. He is standing erect and facing squarely the receiving station which is represented on the chart. The flag is held vertically in line with center of head. This position with three motions constitutes the Wigwag System.

On the chart at the left is shown the first motion, which represents the dot. To make this motion the flag is waved from position to right of sender and back to position. This mo-


FIG. 6
Members of a U. S. Marine Signal Corps Company wigwagging from a signal tower erected on roof of a building at Vera Cruz, Mexico.
Courtesy of U. S. Marine Corps

tion is always made in a plane at right angles to the line connecting the two stations as shown in center of your chart.

The second motion shown on right of chart gives you the dash and is made exactly as above only to left of sender.

The third motion shown at bottom of the chart is made by a wave of the flag from position directly in front of sender to your feet, and instantly returning to position or ready. This third motion represents front or interval. One front motion is given at end of each word, two at end of a sentence and three upon completion of a message. In making a letter of the alphabet say the letter Q four strokes are made ; i. e. LEFT LEFT RIGHT LEFT. It is not necessary to pause at position in going from extreme left to right or vice versa. However, a slight pause should be allowed




at the completion of each letter. Then continue to finish your word and to give the front signal.

A great deal of practice is necessary to become a rapid sender by the single stick flag. Care should be taken not to foul the flag on the staff, as the full fly of your flag should always be seen by the receiving station. This is sometimes hard to do, especially on a windy day, but experience will teach you how it is best to avoid a troublesome situation.

The U. S. Army uses two standard outfits for wigwagging. These are known in the Signal Corps as kits. The two-foot kit contains a three-jointed hickory staff, jointed with brass screw ferrules, and when fitted together makes a strong pole 69 inches long. The flag is made fast to pole by means of three ties of tape. These are looped through brass eyes on pole.

Two flags, the size of each being 2 feet square, are provided, one of bright red material with a white center 8 inches square and the other white with red center. The flags and pole can be packed in a canvas kit about 2 feet in length.

The other outfit used is the "four-foot kit." In this outfit the

FIG. 7
Boy Scouts sending a message by two-arm semaphore.
Courtesy of Boy Scouts of America


pole is heavier and when jointed is 12 feet in length. The two flags are 3 feet 9 inches square with 12-inch centers; they are of alternating colors, red and white, as in the smaller outfit.


The size of the wigwag flag to be used depends entirely on the distance you want to transmit a message, and whether or not the receiving station is equipped with glasses. Under ordinary conditions a flag of 18 inches or 2 feet can be read a distance of one mile without glasses and two miles with glasses. This is the extreme limit for a flag of that size.

Nearly all single stick flags are made up of a combination of red and white colors, as these colors usually give greatest contrast. Red and orange is also a good combination.

Always select the color of your flag so as to give greatest possible contrast against the background. The white flag should never be used where your background is a snow-covered hill or light sky; but if sky is heavily clouded a white flag will prove best. The red flag should be used against a light background, of course. As some backare very de-

FIG. 8
Boy Scouts of Ansonia, Conn., sending a long distance wigwag message at sundown.
Courtesy of Boy Scouts of America


ceiving at times, it will take a little study on your part to determine the proper flag to use for particular conditions.


At night the signal flag is of no use; the substitute is either the torch or lantern.

If you are out in the woods and want to send a message at night to an adjoining camp and have no torch or lantern at hand it is great fun to use firebrands. Selected sticks of dry wood can be placed in the camp fire and lallowed to burn a minute or two. The signalist can then send a message to his comrades. It will surprise you to learn the distance you can send messages by this method. Care should be taken to get out of range of your camp fire, as its reflection would hinder the receiving party. Signaling at night is always subject to

FIG. 9
A U. S. Marine semaphoring, Haiti, West Indies. 
Courtesy of U. S. Marine Corps


FIG. 10
U. S. Army Signal Corps on Mexican Border

more adverse conditions than by day. Therefore it is advisable to send messages much slower at night. Where the distance is great, an additional light should be placed in line with center of your body and about 2 feet from the ground to act as an indicator or point of reference in the motion.

About the most practical way of wigwagging at night is to  use two lanterns, one for the indicator and the other for transmitting. Care should be given at night to the front motion, so as to make it distinct. This motion can be simplified somewhat by moving the lantern vertically from your head to your indicator light. For long distances you can fasten a lantern to a pole.

Go to Gilbert Signal Engineering Part II    or   Back to the A.C. Gilbert Collection

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