Page:The Granite Monthly Volume 1.djvu/113

 AN OCEAN CABLE.

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��AN OCEAN CABLE.

��BY G. H. JENNESS.

��The laying of the Direct United States Cable to the coast of New Hampshire has been the means of calling the attention of many of onr citizens to the mysterious process of ocean telegraphy. The sub- ject is one not familiar to most people, and comparatively few have any intelli- gent idea of its modus operandi. We have become so familiarized to the "click" of the telegraph at all our depots, oflices and hotels that it is difficult to conceive of reading a message that gives no sound. It must be borne in mind, however, that the means, methods and instruments of land and ocean telegraphy are radically and totally dissimilar. In order to com- prehend the difference, it will be neces- sary to consider briefly the Morse or land telegraph, and also the nature of its mo- tive power — electricity. Of the latter, it is sufficient to say that nobody knows what it is — we can only deal with its phe- nomena as witnessed under varying con- ditions. In its terrific form, we see it in the passing shower of the midsummer afternoon, when the descending bolts of lightning shiver houses and trees, and in- stantaneously annihilate animal life. In gentler moods, it appears in the rustle of a silk dress or the stroking of a cat's back.. It seems to pervade nearly every- thing, but from whence it cometh or whither it goeth is alike a mystery to prince and plebeian. For the purposes of telegraphy and experiment electricity is usually generated by chemical action. The "battery" used in telegraph offices is made by placing zinc or copper in glass or earthen jars partly filled with water, into which is dropped common blue vit- riol or sulphite of copper. The vitriol dissolves and "precipitates" upon the metals, and in some unknown way gen- erates the mysterious agent we call elec- tricity. This is the motive power that is

��used in all telegraphs and cables, of what- ever name or nature. Now for the meth- ods of conveyance ! In the land tele- graph the "click" is made by a bar of steel that is attracted to and let go by an electro-magnet. An electro-magnet is a rod of soft iron, bent in horse-shoe form, and closely wound with copper wire. When connected with a "battery" it is instantly endowed with the power of at- traction, and as instantly loses it when the connection with the battery is sev- ered. It will attract a bar of steel just as a common "horse-shoe" magnet will pick up a needle or a steel pen. With the common magnet there is a little bar of steel which we call an "armature." When the magnet is placed near it, it is drawn to the ends of the bent iron and held there by the power of magnetic at- traction. The natural magnet will at- tract, but it won't let go 1 The electro- magnet, or a magnet by electricity, will attract or let go at the will of the opera- tor. Put the electro-magnet on one end of your table, and the bottle or jar con- taining the battery on the other, connect and disconnect it with the wires, and you can see at a glance how a rod of iron wound with copper wire is a magnet one moment and not a magnet the next. Put the battery in Portland and the electro- magnet in New Orleans, connect them with a wire, and the result is all the same. Put a pin on the end of the steel armature, and some clock-work to regu- late the passage of a strip of paper over it, and you have substantially the Morse or common land telegraph. The knob or "key" which the operator presses down with the finger is the means used to connect and disconnect the magnet with the battery, or, as the electricians term it. to "break the circuit." Thus every touch of the key produces a correspond-

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