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the party may for a while lose sight of all signal points. The forward rodman selects a station, and that station is occupied by the party and instrument. The rear rodman occupies the station just left, and the table is oriented upon his rod. The forward rodman again goes ahead, selects a new station, the party moves, and again orients upon the rear rodman, who is standing over the station just left. Two miles are sometimes traveled in this way, without sight of a signal; but more than that, it is not wise to attempt. Of course, soon as any known signal is in sight, the orientation is checked by its means; and if it be much out of the way, the charting is either done over or corrected by other means.

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Plane-Table Signals It not infrequently happens in river work that a bend or a bay may be out of sight of signals. In this case, a temporary signal called a plane-table signal is erected, which is is in sight of the other signals, and which can be seen from where the work is to be done. The

called the three-point problem. From the shape of the triangle, the worker can make a better guess of the proper location of the true point, which he does, and orients all over again. The triangle of error this time will be smaller. A skillful worker can get the true point in two

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RODMAN ON STATION, WITH TELEMETER ROD. The divisions on the rod, read between the cross-hairs on the telescope, indicate distance between rod and telescope.

point is selected, the table set up, and all made ready for work as before. But the table cannot be oriented, because there is no point upon the chart corresponding to the location of the table. The man in charge, however, has a pretty definite idea as to where he is, and makes a tentative point upon the chart with his pencil, proceeding then to orient the table with that as a base. Of course this operation is not accurate, and, as a result, the lines from other signals form a triangle around the point he has selected. This triangle is called the triangle of error, and the determination of the correct position is

or three trials with surprising accuracy. Once the true point is determined on the chart, that spot upon the land is as effective for work as if it were a triangulation signal. A temporary signal is erected over this spot, and work done from it exactly as if it were a permanent structure.

The accompanying pictures will give one a better idea of what a signal is than any written description. A permanent signal is a triangular structure of heavy timber, anchored to the land by means of heavy stakes driven deeply into the ground, and having a flagstaff projecting upward from its center. The sides of the

triangle are boarded together for security, and the peg and bottle placed beneath it as already described. A temporary signal is usually made of a stripped tree, braced with poles and anchored; and bears upon its end a flag, and perhaps a lozenge, made of cloth and tacked down. It is very important that a signal be perpendicular. If it is not, it will form an angle with the cross-hair in the telescope,

"ALL RIGHT!" Signaling to rodman to move on.

and not be as accurate (although of course the hairs can be turned to any angle) as if it were straight. So, when a signal is erected, it is plumbed before being fastened; the man in charge holds a plumb line on it, and directs those who are putting it up how much to one side or another it must go before being fastened.

Accuracy Never Sacrificed through Hardship

A plane-table party often endures considerable hardship in its work. Mosquitoes are thick along certain parts of the coast and rivers, and bother the workers -who need their hands-in no inconsiderable degree. The weather is often either very hot, under the broiling sun, or, later in the year, very cold. There is a good deal of getting wet in the work -from high seas for a small launch, and from wading in along a shallow bottom

from the tender in which the instruments are conveyed from the launch to the shore. Nevertheless, the parties are all imbued with the idea that their work. must be done well though the heavens fall; and indeed, if it were not for the painstaking care in this work, who knows what wrecks and disasters might result? Your mariner accepts without question the information furnished him. on a chart, and runs his craft accordingly. If any glaring errors have been. made, lives and property may be sacrificed. The writer has had some experience with the work, and met many men engaged in it, and he has yet to see one who did not take the work with the necessary seriousness, or who counted any discomfort or hardship as of any moment whatever against the proper execution of the work.

When the field work of a chart is finished, it goes to the home office, where it passes through a great deal which is of much interest before it is finally issued in the form of a chart. But that work, and also the hydrographic work, are separate stories, of surpassing interest of themselves, but not belonging, properly speaking, to a consideration of planetable work.

What we have told is but an outline. There is more-much more-to the full use of a plane table than we have indicated, but the present story covers the most common practice and the principal use of the instrument. To attempt, however, to write a plane-table manual in a popular article of this length, would be as absurd as to try to explain the science of algebra in five pages of a magazine.

The plane table is unique among surveying methods, inasmuch as it draws the map from nature's model absolutely without notes, all work being done on the sheet in the field. With it, all is sufficiently accurate at the scale at which it is employed, and its use has been brought to a high state of perfection in this country. Without it, the making of charts would be a much slower and more laborious process than is at present the case; and the development of the records of our water lines would be correspondingly retarded.

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How These Arteries of Submarine Communication are Constructed, Laid, Operated, and Repaired

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By P. T. McGRATH

Staff Correspondent, The Evening Herald, St. John's, Newfoundland

MONG the agencies for the electrical transmission of intelligence, the submarine cable is unique, playing a far more important part in the economy of commerce and diplomacy than the land line and telephone. When, in 1844, Morse demonstrated the feasibility of telegraphing overland, the inevitable corollary was the devising of some means whereby rivers, lakes, and, ultimately, seas and oceans, could be bridged. Scientists quickly conceived the idea of submerging a wire adequately insulated, though the practical difficulties in the way of securing an effective insulator took years to overcome. Ultimately, a copper wire, covered with gutta-percha, was laid in Portsmouth Harbor in 1846. Dover and Calais were connected below the bed of the English Channel in 1850; Harwich and The Hague were joined under the North Sea

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ing it a sea serpent, he severed it with an axe. Many Newfoundland fishermen thought the first Atlantic cable would be an excellent thing to utilize for mooring their boats.

The development of submarine cables. has been remarkable, both in their widespread use and in their enhanced efficiency. The North Atlantic is now spanned by fifteen cables, and the Pacific by two; and other seas have an ample quota besides. The total is 1,764 distinct cables, with an aggregate mileage of 211,000, interlacing not alone the continents but the most widely separated insular areas of the world, until only the remote and and unpeopled Arctic and Antarctic zones are without this potent accessory of modern civilization. Even as this is written, it is proposed to lay a cable between Iceland and the Orkneys, there connecting with the British Postal Telegraph system of cables and land lines, so that, by an extension later to Greenland, or by the use of the wireless medium, it may be possible to follow the daily movements of future seekers for the North Pole.

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How a Cable is Made

The cable is merely the land line completely insulated for its whole length (the water being so potent a conductor of electric force), and with its metal core of a substance affording the highest "conductivity," as no repeating stations are possible between land and land. Copper is the best known conductor for cables, and the electrolytic quality is almost absolutely pure. It is now being used for land lines, its great cost formerly preventing this. Gutta-percha, in the same way, is the best insulator-not absolute indeed, but, according to some authority, having a conductivity so small that "it may be said to stand in the same relation to copper as the rate of a body moving through one foot in 6,700 years is to the velocity of light, which attains 186,000 miles in a second."

In the early days of cable-laying, these problems had all to be solved by the electricians of the period-Faraday, Thomson, Whitehouse, Wheatstone, Muirhead, and others. The "velocity of propagation" of the signals involved the efficiency

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and economy of the cable. Faraday determined the electrical capacity of the cable, the unit in which that is now measured being ever since termed the "farad." Thomson found a mathematical definition for the capacity and its dependence on the dimensions and insulating material. Whitehouse proved that large battery power was not needed for long cables, as the Irish pilot proved the presence of rocks-by working the first Atlantic cable with such an electrical charge that he forced it through the insulation and destroyed that medium, rendering the cable valueless. Wheatstone invented the automatic transmitter; Thomson, the siphon recorder; and Muirhead, the duplexing system. Edison concurrently invented a quadruplex method of land telegraphy, of which, semihumorously, he says himself: "Twenty-five

years ago I sold the system to the Western Union for $30,000, and spent the whole of it in experiments for making a wire to carry six messages instead of four. I did not succeed; so that, financially, I am worse off than I would have been had I never invented the quadruplex system at all."

Cables are made chiefly in England, though France, Germany, and Italy are

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LANDING-PLACE OF FRENCH CABLE, ST. PIERRE.

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