The Science Notebook
Gilbert Signal Engineering - Part 2

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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.

Pages 26-50


A good torch can be made by nailing an old tin can to a pole about 6 feet long; stuff the can with old rags or waste; pour over these a little oil and light with a match. This will give you a torch that will burn long enough to send any message of reasonable length.


The beam of a searchlight may be used for wigwagging at night and in the U. S. Navy it is very frequently used. The rays of the light are directed vertically and swing from right to left to indicate the dots and dashes of the General Service Code. All motions are the same as in the single flag Wigwag System.


Chapter III

Now that you have become familiar with the General Service Code and one method of sending it, a few rules can be given that will be of help in all systems of signaling. Many bits of this advice may sound military, but you may well take heed of it for it is essential to practical signaling more so if you are a Boy Scout or some day have occasion to work with a military organization.

Signaling, like all professions, has its established terms and a correct plan of procedure. To gain a full knowledge of signaling it is necessary that you become accustomed to handling a message correctly.

A Signal Station consists of one or more signalmen operating as a unit and ready at all times to send or receive a message. The station can be either temporary or stationary.

The Home Station is station to which you are assigned.

The Sending Station is station sending message.

The Receiving Station is station receiving message.

To Call a station, it is the usual plan first to attract attention. This is done in the various signal systems as follows :

1. Wigwag system: Succession of dots and dashes.
2. Semaphore system : Waving flags at attention.
3. Sound system: Succession of dots (or toots).
4. Heliograph system : Long and short flashes.
5. Ardois system : Display of four white lights.
6. Radio system  - . - . - .
7. Buzzer system: Station call letter.


8. Telegraph system: Station call letter.
9. Flash light system: Short flashes or dots.

In addition to attracting attention, if the call letter or letters of the station you desire to communicate with are known, the signal representing them should be made at intervals. It is very important that each signal station has a call of one or two letters. Any letters can be adopted such as X or XY. This is essential for the reason that you may be facing and within signal distance of two or three stations at times and want to send only to one of these, individually. Note: If call letter is unknown, use the letter A.

The Receiving Station always acknowledges your call by making R and its call letter. After this acknowledgement you are ready to proceed with the message.


The plan of the message varies at times, according to the organization; however, all messages are divided in a general way as follows:

1. Preamble.
2. Address to.
3. Text of message or body.
4. Address from or signature.

The preamble of the message is reserved solely for use of signalmen dealing with the message. The preamble or introduction of a message consists of the serial number of message and time message is handed in at station and accepted for transmission.

All stations use serial numbers in handling messages, beginning with number one and so on up for each twenty-four hours, after which a new series is started. Next comes the call letter of sending station or office of origin, the signalist's personal signature (all signalmen must use a personal signature as, J. J.


for John Jones, etc.) the check of message (number of words in body of message), and the class of message.

To arrive at the exact number of words in the body of a message this rule is followed: Include in count the address after TO and all words in body, including the address following FROM, but do not count FROM or SIG. if that term is used by signalists. Abbreviations, figures and names of cities and states should be counted as one word, for example : C X K (get reply) is one word; South Chicago, Illinois, or So. Chi. Ill., is counted as two words ; and one-quarter as one word.

The message usually indicates whether it is official business (OB) or official message (OFM) as collect, or paid message, urgent, etc.

The Address of a message should always contain enough words or information to insure its delivery.

The Address FROM should convey the same amount of intelligence.

The Double dash - . . . - of the General Service Code is
always used between the preamble and address TO; between the address and text; and between text and from or signature.

The following is a message handed in at a signal station at Brown's farm (call letter B) at 10 A. M. to be transmitted to station X Y (Smith's Crossing). Signalist John Jones (J. J.) takes the message:

(To) Bill Smith,
Smith's Crossing.

Get your gang together and meet me at the Stony Creek Bridge at 2 P. M., I will bring the bunch, don't forget your skates, ice is one-quarter foot thick.

(From) Harry Brown, Brown's Farm

Get reply to this message. (C X K)


After Jones checks the message he finds it contains 38 "signal words." He numbers it 8 (as it is the eighth message he has sent that day from his station) and decides to send it by single flag wigwag. After getting attention of station X Y he proceeds to send as follows :

8 ( - - -. . ) interval or front TEN front A. M, front, B (Brown's Sta. call) front, C.K. 38  (message check) front, JJ.   (Jones' signature) front, OF (official message) front (- . . . - ) (double dash) TO: front Bill-Smith-Smiths-Crossing-get-ur-gang-together and-meet-me-at-t-Stony- Creek-bridge-at  2 (. . - - -  )-P.M.-I-will-bring-t-bunch-don't-forget-ur-skates-ice-is (- . . . - ) (double dash used before fraction)1           (. - - - -  ) (- -  . . - .) (indicating fraction bar) 4 (. . . . - ) foot thick (- . . . - (double dash)-SIG.-Harry-Brown-Browns-Farm - C X K (get reply) - (. - .  - . -) (cross) or (. . . - . - ) (meaning end of work).

Station XY acknowledges receipt of message by O.K. or . - .  (R). The receiving station has a record of this message as sent above and the transaction is complete.

Of course, if you are not an expert signalman, to lessen liability of errors, it is best to spell out all numerals, fractions and abbreviations.

A message handed in at a signal station should always be looked over, for an omission of one word may change the meaning of the whole message. The advantage and importance of checking by sender and in the recheck by the receiving station can be seen at once.

Both sending and receiving stations should record on the message what system was used in handling it. The date should also show, although the serial numbers, in a measure, indicate


the dates. As you will recall, they are changed every twenty-four hours.

In military organizations all messages are considered strictly confidential.


You have been told that a signal station consists of one or more signalmen operating as a unit. Where there is more than one, each must have his duties to perform; therefore, it is advisable where three boys are operating a sending station to know just what each boy's duty is.

First Boy or Caller takes charge of the messages, checks same and makes proper entries. When message is ready to send he
calls the word or group to

Second Boy or Sender whose duty it is to send the message as called. His other duty is to see that his sending equipment is always in good condition.

Third Boy or Answer Reader reports signal as being answered and watches for interruptions from receiving station, using binoculars when necessary. Note : Should four boys be operating a station, the fourth boy will act as a messenger.


At times signal units have a good many messages on hand to dispose of and have these messages in course of transmission when a very important urgent signal is handed in. It then becomes necessary to make the Break Signal, which is the attention sign by all systems. As soon as the break is acknowledged, proceed with the more important message.

The Answer Reader should always be on the lookout for


signs of error from receiving station and report to sender what portion of message has been missed.

The duties of these boys at a receiving station are similar.

First Boy, Reader (with binoculars), reads each letter, sign or numeral, calling out group on ending of each word, etc.

Second Boy, Answerman, stands by to make any necessary interruptions and to answer signal as required.

Third Boy, Writer, writes on signal form each group or signs as called out by the reader.

The first boy must be an expert on signals, for it is his duty to take charge of the signal unit. When his station is acting as a receiving station, it is his business to read correctly all messages. He should enforce a certain amount of discipline around the station, and not allow any unnecessary talking, etc., while signalmen are operating,


The intervals of the General Service Code were purposely omitted in Chart 2 so as not to confuse you with their secondary meanings. They are as follows :

Interval Double Interval Triple Interval
. - . - . .  . .  . .
(same as period)
. - . - . -
(same as cross)

Intervals are expressed as follows in the various systems:

Interval Double Interval Triple Interval
1. Wigwag front motion  (twice) (three times)
2. Semaphore flags crossed or
machine closed
2 chop-chop signals 3 chop-chop signals


Interval Double Interval Triple Interval
3. Sound

 . . . (short taps)
long blast

. .   . .   . .
. .   . .   . .

.   . .   .   . .   .
.  -  .  -  .
4. Radio
Flashing light
Buzzer and
(space) . .   . .   . . .  -  .  -  .
5. Ardois .  -  .  -  (twice)  (twice) {three times)


You have been informed that, when a message is handed in at station and accepted for transmission, a record of the time is made and sent in the preamble. This code time serves to show how long a message has taken to pass through the hands of the signalmen.

In order to save time to spell out or to send code time by numbers, the Letter Clock System is sometimes used.

Chart 4 gives you the letter clock, which is an ordinary clock face with letters placed against the hours. The twelve hours are denoted by the first twelve letters of the alphabet, omitting the letter J. These letters stand not only for the hours but also for periods of five minutes; for example: A would be one o'clock and five minutes past any hour, B two o'clock and ten minutes past any hour, and so on. AA would mean one five, AB would mean one ten. To denote intermediate minutes the letters RSWX are used in every period of five minutes. Thus MR means one minute past twelve; MS means twelve two.

The hands of clock shown on your chart show time to be four minutes past six o'clock and the letters that denote that time





are FMX, reading in code time 6.04 either A. M. or P. M. as case may be.

Should a message be handed in at a station at exactly noon or midnight it would have to be recorded by code at one minute past to avoid confusion. The message handed in at noon would be put in code as MR P.M. and at midnight MR A.M.


Chapter IV

The word semaphore is derived from the Greek word seema, meaning a sign, and phero, to bear or carry. This system is sometimes called brachial telegraph, meaning telegraphing with arms,


The two-arm semaphore machine is used in permanent stations only, as it is not a portable piece of signal apparatus.

The semaphore machine is authorized for use of the U. S. Army at fixed stations and is used on all the larger ships of the U. S. and other navies.

This semaphore machine has two arms or vanes for forming the characters of the code and a third arm or indicator displayed on right of sender (on left as viewed by receiver) as a point of reference to motion.

Semaphore machines are usually about 8 feet high, with arms of 2 1/2 or 3 feet. The arms are operated by two levers which are placed on the machine at average height of elbows of the body. An additional lever operates the indicator arm.

The machine is painted black or gray, while arms and indicator are colored a light yellow.

For night use the machine is fitted along entire length of the arms with electric lights. The indicator is used by day only to indicate direction of sending; at night, instead of the indicator, a red electric light is used at top of machine. This light is screened to rear, and if machine is facing receiving station squarely it will





not be seen. Semaphore machines are mounted on a pivot so as to turn in any direction.

Chart 5 will show you alphabet of the semaphore code expressed by a two-arm machine.

In addition to the two-arm machine used by the U. S. Army and Navy there are several other types of machines, some having as many as six arms. The most common of these is the four-arm semaphore used for transmitting distant signals by the International Code and by fixed shore stations to communicate with ships of all nations. A great many of these semaphore stations are found on the coasts of Great Britain, France, Italy, Spain and Portugal.

Of course you are familiar with the type of semaphore used by all up-to-date railroads, but do you know what these signals mean?

A vertical position of arm means safe at night a white light is displayed. A horizontal position of arm means danger at night a red light is displayed. The intermediate position of the arm means caution at night a green light is shown.


The method of semaphoring by hand flags is used in both Army and Navy, Boy Scouts, Girl Scouts and nearly all organizations using signals.

This system of signaling has been more highly developed in the U. S. Navy than in any other place on account of its rapidity and simplicity for the exchange of messages between ships of the fleet.

In the Army and other military organizations this type of signaling is somewhat limited on account of short range. The usual range for hand flags of 18-inch size is about one mile with the naked eye, and is always dependent upon your background














and the light. Much greater distance is possible, of course, with use of a telescope.

The size of flags used by the Army are 18 inches square, divided diagonally into two parts one red, the other white. The field and coast artillery use the same size except as to colors, which are scarlet and orange. The arrangement is a 9-inch square in center of scarlet and a border of orange for work against dark background. For light backgrounds the order is reversed. The staffs used are 24 inches long.

The U. S. Navy uses flags from 12 to 15 inches square of blue with white square center for light backgrounds. For dark backgrounds, a flag of red and yellow colors, arranged diagonally is used.

Now turn to Chart 6 and study the different positions. The boy is holding the flags so as to make the characters of the alphabet. You will notice that all positions by hand flags are the same as by machine, excepting the interval, which is made by crossing flags in front of sender's legs.

The quickest way to learn semaphoring is to practice with one of your friends. After memorizing all the characters of the code, send simple words to each other and later short messages.

In making the characters all motions, pausing slightly following each, should be sharp and distinct to avoid confusion.

At the end of a word the interval shown on the chart and already described is used. At the end of a sentence the double interval, two chop-chop signals, is made. At the end of the message a triple interval, three chop-chop signals, is used.

The chop-chop signals shown on your chart are made by placing both arms vertically to right of sender and by working flags up and down in a chopping motion.

Additional symbols found in your chart are attention or cornet, numerals follow, signals follow and letters follow.


This attention signal is, of course, used to get attention, and is made by agitating the letter R.

The numerals follow signal is made by crossing flags over head and is used to designate the fact that you intend to use the numerals which are expressed by secondary meanings of your alphabet letters A to J as shown on chart. The numerals are made by semaphore in this way by all organizations except the Navy, where regulations require them to be spelled out in full. The interval must be used following each numeral.

Signals follow is made by reversing the letter L and is used to designate the fact that a code message or secondary meanings follow.

Letters follow is used only by U. S. Army and Navy and is made the reverse of the letter T. It signifies letters will be used to spell words.

A great many of the conventional signals and abbreviations given in your General Service Code can be adopted for semaphoring. To indicate an error in semaphore the letter A is used as in the General Service Code. As A already has a secondary meaning (the numeral one) it is necessary to agitate your flags a little.

The conventional interrogatory signal is made by agitating the letter O.

In sending an official message by semaphore the same rules are followed as given in preceding chapter.

No punctuation marks are given in the semaphore code and if used they must be spelled out.

Do not slur your letters in semaphoring but make them exactly as shown on charts. However, now that you are becoming a real signalman, it will not do you any harm to know that experts at semaphore signaling sometimes deviate from the regular motions. To explain this in a practical way, spell the following word without moving your right arm, after mak-


ing the first letter of word MANILA. Spell BED also with right or left arm only.

In semaphore signaling when sender makes an "end of word" sign, the receiver acknowledges this, if the message is understood, by extending his arms horizontally and by waving them until the sender does the same and message is finished.

By machine, the receiving station fixes his call letter stationary until the message is received and understood and then the machine is closed.


Chapter V

SOUND SYSTEM. As early as the 17th century attempts were made to establish communications by artillery and musketry firing. The system of sound signaling, came into use at this time.

The sound system is based on the General Service Code and is used more commonly by the ships of the Merchant Marine and the U. S. Navy. However, due to its aptness to cause confusion, it is rarely used by ships except in cases of emergency, such as in fogs or when a breakdown of other signal apparatus occurs and only in regions unfrequented by other vessels.

Messages are sent by the sound system by use of steam whistle, foghorn and bell.

When the steam whistle is used, messages are spelled out, except in the case of the U. S. Navy, which uses the Navy Code.

The intervals by all methods of the sound system are expressed as previously given in Chapter 2, under intervals. You will notice a difference in signals for interval in case of the whistle or bell.

In the case of the whistle one long blast represents the dash and a short one for dot ; but in use of the bell a continuous sound cannot be made, therefore it is necessary to use two strokes to make a dash and one stroke for a dot.


The Navy has lately adopted a code for signaling by bugle or trumpet; this code was invented by a high school student of West Roxbury, Mass. The code is given you in Chart 7. No





special musical knowledge is necessary to sound the characters of the alphabet and numerals, except to acquire what is known by players of wind instruments as the "lip," which comes very easy with a little practice on a horn.

You will notice the letters of code are expressed by not more than four notes and all numerals by five, either eighth or quarter notes. The relative value of the eighth note to the quarter note is one-half. Therefore an eighth note is made by a short blast on the horn and the quarter note by a blast twice as long. The eighth notes are the ones having the small pennant at tip of the stem.

Signals can be sent by this method in any key, but it would be very confusing to change key or pitch of your tone in middle of message. Avoid slurring the notes and give special attention to length of blast signified by eighth and quarter notes.

Intervals between words in Bugle Code are made by allowing a space, and the end of a message by one high note.

To call a station by Bugle Code blow long blasts followed by station's call letter. If call letter is unknown, use the letter A which is common in all signal systems when a station call is not known.

To acknowledge receipt of a message blow one long note.


All boys are familiar with the police whistle or similar type carried by Boy Scouts. The cost of these whistles runs from 15 to 50 cents and every boy should possess one for signaling or emergency use in the woods.

To signal a message by pocket whistle use the General Service Code.

The special conventional signals by whistle used by the Boy Scouts are as follows:


1. One long blast means "Silence," "Attention," "Look out for my next signal," also used in approaching a station.

2. Two short blasts mean "All right"

3. A succession of short, sharp blasts means "Rally," "Come together," "Close in."

4. A succession of long, slow blasts means "Go out," "Get farther away" or "Advance," "Extend," "Scatter."

5. Three short blasts followed by one long one from scout master calls up the patrol leaders i. e., "Leaders come here."

6. Three long blasts means "Danger," "Look out."

7. A succession of alternating long and sharp blasts means "Mess Call."

All whistle signals should be obeyed as quickly as possible, no matter what work you may be doing at the time.


The equipment used to send messages by this system is the electric blinker, operating with a telegraph key, and the lantern or searchlight equipped with shutters.

The electric blinker is authorized for use in the U. S. Navy and is also used by many other navies and merchant vessels. The electric lamp is usually placed at the peak of the foremast or on yardarm and operated by a key from bridge of ship. Incandescent lamps, 110 volts, are used. These are used as a night system only and, like the other systems, has its disadvantages, especially in foggy weather when used in a locality where a group of ships are at anchor displaying their many lights.


For sending messages by blinker the General Service Code is used.


The standard night signal equipment used by the Army is the acetylene lantern.

Acetylene is a pure hydrocarbon gas, and is produced in the signal lantern by bringing water into contact with calcium carbide. The illumination resulting is about 1900 candle power and, with the exception of the searchlight, the acetylene lantern furnishes the most powerful form of night signaling. The range obtainable by this type of lantern is as much as ten miles with naked eye, and with a 30-power telescope the flashes can be read for thirty miles.

On dark and cloudy days this lantern can be used for day signaling at a distance of one-half to three-quarters of a mile.


The most powerful night system used is the searchlight, which is equipped with a shutter and operated by a key. This method of signaling is used by coast artillery corps and most commonly by the Navy. While it is essentially a night system, it is also used in day sending, and ships at sea in ordinary weather have been able to send messages for distances up to ten miles.


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

The sun being the most powerful light in existence, heliograph flashes can be sent farther than by any other method of visual signaling. When the day is clear and the sun's rays intense,

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