Page:Popular Science Monthly Volume 91.djvu/626

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��by turning a small crank by hand, but it is not difficult to gear a small electric motor to operate it and thus to afford true automatic operation.

Any sort of automatic transmitter can be made very helpful in learning the code. The apparatus is not very expensive, and if five or six students combine to purchase one together the cost to each individual becomes extremely low when compared with the benefits secured from having a tireless sender of perfect Continental Morse signals which will give practice as long as it is wanted. Fig. 1 1 shows how to connect the automatic sender at one of the stations of a multiple-station buzzer-telegraph line. The balance of the stations are wired in ac- cordance with Fig. 8. The automatic sending station of Fig. 1 1 may be chosen to be somewhere near the middle of the tele- graph line, so as to give about equal strength signals at both ends; the line wire extending to the other instruments is in- dicated by the broken line at the top of the figure. The telephones T are shown shunted by the signal-intensity regulating resistance R, and connected between the line wire and the vibrator post contact of the buzzer Z. The two outer terminals of the buzzer are connected in series with the battery B, a single-pole double-throw switch S, and either the hand-sending key K or the auto- matic transmitter A. The armature post of the buzzer is connected with ground at E. When the switch 5 is in position / the hand key is connected, and signals may be trans- mitted in the usual way. When the switch arm is in position 2, the key is cut out and the automatic transmitter placed in circuit. The signals which it sends out are trans- mitted both up and down the line, and may be copied simultaneously by all the students at their respective home stations.

Morse Practice on the Buzzer Line

By arranging a definite time schedule for running the automatic sender, it is possible to work out a scheme of daily Morse practice at gradually increased speeds, until finally all the learners are able to write down messages at a speed of from twenty to twenty-five five-letter words per minute. To make the practice comprehen- sive it is necessary to arrange for periods of sending practice for each of the stations, in which one student sends messages or press notes from the newspapers and all the others copy his signals. The messages as copied by each one should be carefully

��Popular Science Monthly

��compared with the original as it was sent out; errors in receiving can be located by reason of their appearing on only one of the copies, while errors in transmitting should show up in all of the copies. Practice of this sort, varied by the exchange of mes- sages between various pairs of stations on the line, will give the most valuable training which it is possible to secure outside of actual radio telegraphy.

In the first article the Morse symbols corresponding to the twenty-six letters of the English alphabet were given. Fig. 12 shows the numerals and the more usual punctuation marks. These should all be memorized and used in the message practice. Entire familiarity with the code as thus completed will come with the daily sending of dispatches, and a few months of this work should make any apt student a fairly, skilful telegrapher.

In the next article the formal methods of sending messages with full preambles, ac- cording to the International Radiotelegraph Convention, will be explained and illus- trated, and the problems of reading messages and signals through interference from other radio stations and from "static" or atmospheric electrical disturbances will be discussed.

(To be continued)

��The Underwriter's Knot for Flexible Cords

FLEXIBLE cords used to suspend a lamp should be arranged so that there is no stress or strain coming on the binding posts or con- n e c t i n g screws. To provide a suitable holding means, knots should be tied in the cord to make them take all the weight of the socket and fixture from the ends of the wire. The successive steps in tying the knot are shown in the illus- tration.

While these knots may appear to be of no use they are absolutely necessary, not only to relieve the strain, but to fulfill the requirements of the underwriters' code for safety in insurance.

���A knot tied in line in such a way as to take the strain from a fixture

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