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messages each way over one wire, and the telegraph. The sending or receiving the simple pressure of the proper key at of a telegram is to the average family the sending station is all that is necessary a thing of rare occurrence; but it is to be to have the corresponding character hoped that in the future the reduction in printed at the receiving station. The use cost, owing to the greater ease with of the alternating current is also a tribute which messages may be sent, will proto the originality and foresight of the in- mote among the people a more extended ventor, since it lends itself very readily use of this means of communication. It to the needs of telegraphic communica- would be within the bounds of probability tion. The future will probably see all to say that we may some day even transoverhead wiring banished; and the elec- mit whole letters by telegraph. trical difficulties which are to arise from The Rowland machine, in its present
commercial form, is divided into what are called the line-unit and the correspondence-units. The line-unit has for its function the operation of the line, and contains the necessary apparatus for furnishing the signaling current, impressing the signals, etc. This unit is identical in form at each end of the line. The correspondence units receive and transmit the messages; each consists of a transmitter, a receiver, and a home recorder. The transmitter is a universal typewriter keyboard; the receiver an automatic page-printing machine, which records the message in page form on a telegraph blank, ready for delivery; and the home recorder a printed tape passing along a scale before the eyes of the operator, giving a duplicate of the message sent out. There is another correspondence unit at the other station, which is the twin of the one just referred to. These two send to each other, and receive from each other, the signals going
continually over the line, which are rethe placing of wires underground and in corded exactly as a typewriter records its cables will be more easily overcome than letters upon a page. The operator, by with a direct current.
the depression of certain keys, lines and It is hard to predict the far-reaching spaces as though he were operating an effect that the Rowland system will have ordinary typewriter. A red light takes on the telegraphic communication of the the place of the typewriter bell, the carworld. The messages, by automatic rep- riage being backed and the light extinetition, may be transmitted thousands of guished by the pressure of a key. When miles; and this advantage, combined with the end of a message is reached, a quickthose of cheapened service and greater shifting device throws in a blank section facility of transmission, will undoubtedly of the paper before the next message is put into direct communication great begun. In fact, the operator's knowlworld centers which have hitherto com- edge of his printer's movements is so acmunicated with one another only by long curate that tabulation may be done. Specand circuitous routes. It has also been imens of this character of work have been found that the system, when once well transmitted over actual lines 500 miles in established, has partially superseded the length. These correspondence-units are mails and the telephone. It will be neces- instantly and easily detachable, and if one sary, however, to educate the public to a gets out of order another can immedirealization of the latent possibilities of ately be substituted for it.
To understand the system in all its de- Every revolution of the brush will have tails, requires considerable study. The this same effect, provided the flow of curmost that can be done in an article of so rent through the coils is always in the limited a scope as this, is to show the same direction. But if the particular imbare principle upon which the machine pulse of current received by this relay is works—the application of the alternating reversed in direction, the magnetic effect current to the sending of signals.
produced in the coils will be opposite to The figure represents the end view of a that in the case referred to above, and the commutator which has a brush traveling over its surface. This brush has a wire running to a source of alternating current. The segments of the commutator have relays connected to them, one of which is shown in the diagram. It will be seen that as the brush makes contact with the segment connected to the coils of any particular relay, the current can pass through the coils of that relay and back to its source. Suppose the motion of the brush and the alternations of the current to be so adjusted to each other
End View or COMMUTATOR. that the current will change in direction
Showing connections whereby circuits are opened and each time the brush passes from one seg
closed in sending messages. ment to another. This will cause each pair of coils to get a momentary flow of tongue will be thrown against its "front current in one direction or the other ac- stop," the contact-point b. If the mechcording to the adjustments. Suppose the anism shown in the diagram is placed at relay shown receives an "impulse" of one end of a telegraph wire, and the imcurrent in the direction indicated by the pulses of alternating current supplied to arrow. This current will cause mag- it are controlled from the other end, an netism to be produced in the coils, which operator might throw the tongues to magnetism, we shall say, throws the their front stops at will by reversing the tongue t against the contact point a. proper impulses of the alternating current. Thus, these tongues might be used erator has the use of the line at rapidly as little switches to complete the circuit recurring intervals. These intervals octhrough electrical mechanism that would cur at each revolution and are 2-7ths of a perform some desired operation, such as second apart, the machine making 31/2 printing a character or backing a car- revolutions per second. The line is duriage. This is actually done in the Row- plexed in the usual manner by the use of land machine. The above case is ideal, polarized relays and an artificial line, so however, and is varied considerably in that the four messages being received at practice. Mechanism is used whereby each station do not interfere to any extent
eleven relays and segments serve to send whatever with the four messages that are the 51 signals from each keyboard, being sent at the same time. whereas the illustrated case would re- The machines are very interesting from quire one relay and segment for each an electrical standpoint. One very striksignal.
ing instance of the delicacy of the reguThe multiplexing is accomplished in lating devices may be referred to here. the following manner. The commutator The Rowland is what is called a synthat receives the impulses from the line chronous system; that is, the moving is divided into quadrants, each contain- parts at the two stations must be kept ing the segments that are connected to rotating at exactly the same rate of the relays controlling one particular speed. This synchronism is maintained printer. These relays receive impulses with such accuracy, by electrical means, only for the time during which the re- between the two line-unit motors, each volving brush is passing over their own running at 1,960 revolutions per minute, segments. The keyboard of the operator that the variation in speed does not who controls this printer at the sending amount to 1-6 of a revolution for days station, is automatically unlocked at the at a time; this with the motors hundreds proper time to enable him to reverse the
of miles apart. impulses of current received by the relays The Rowland machines have been opcontrolling his printer. Thus each op- erated successfully both in this country and in Europe. An experimental one Baltimore. It is one of the modern was made the subject of exhaustive tests achievements whose perfection is due to in Germany, France, and England; and the labors of others besides the inventor. actual telegraphic work is now being The present standardized machine is the done in this country, the operation in all result of the combined efforts of a corps cases being entirely satisfactory and very of skilled engineers and a force of exgratifying in its results. An octoplex in- pert designers. stallation which has been in use in Italy The advantages of the system as they for three years, afforded an excellent il- have been proved in commercial use, may lustration of the advantages possessed by be summed up as follows: the Rowland system during the recent 1. It is operated by employees uneruptions of Vesuvius. All wires in com- skilled in the telegraphic code. munication with Naples except that used 2. It records and checks errors, and by the Rowland apparatus were in- enables these to be easily traced to their adequate. This Rowland dispatched the source. correspondence easily and promptly on 3. The operator attains a higher averone wire, telegrams being transmitted at age rate of speed than the Morse operathe rate of 8,000 per 24 hours.
tor. The Rowland system has been devel- 4. The wire is made to carry double oped without publicity or advertising, the number of telegrams. and at great expense.
The invention 5. The system operates in full capacity promises to reflect great credit both upon through varying weather and at times its birthplace, the Johns Hopkins Uni- when the Morse and others are cripversity, and the place of its development, pled.
Wax-Farming in China
By Lillian E. Zeb
MONG the novel occupa- cargoes in proper time for the hatching-
remarkable feature in con- taken from the field, and the only ones to nection with this industry is that the reach this country so far. Photographs owner's entire crop is produced by the of the strange creature itself, and other free labor of myriads of little insects, characteristic views, are shown and dewhose eggs or cocoons, deposited on the scribed here for the first time. limbs and branches, yield a rich harvest, .. Comparatively little is known of this which is transformed into pure white peculiar and valuable insect of China, wax and marketed at a fair price. Equally though it is found also in Japan. In both odd and fantastic are the midnigł t jour countries it selects different trees to feed
A CHINESE WAX-FARMER AT WORK. He is arranging the little insect workers on the trees in the way that will best produce the strange harvest.
neys of the agile and sure-footed porters, upon. This insect is about the size of a who are forced to hurry along as fast as mosquito. The male has a head nearly possible with their loads of insects on triangular and of a light orange color. their backs, hundreds of miles, across The antennæ are long and composed of steep and rocky mountain passes, ascend- segments, comparatively long, light ing and descending precipitous places brown, and covered with grayish hair. which no animal or conveyance could tra- The first pair lie far apart from the othverse with safety, in order to land their ers. The four wings are long, oval, and