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ONE OF TUE JOY'S OT STRIT; 710 Using a sled and four bullocks to transport instruments to the triangulation station at White Rocki lirginia, which was situated in the mountains, miles from die railroad and approached by 10 road.

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the Pacific coast, and in llawaiithe observed, and 1.102 miles of sounding l'hilippines and laska the datum is lines run, a rock whose head was 18 feet lover, being "mcan lower loin later." below the surface was run upon by the

cruiser Brookly during the naval maTII WIRT DRIG

neulers of that year. The lead-line method of sounding sul In order to discover such obstructions fices to record the law of the bottom litii in much frequented waters a

nell insuihicient accuracy where there are Strument, the wire drag, has bee! extraordinary obstructious; but in a re deviseci. It consists of a long wire, giou like the coast of laine and that ol sometimes more thau mile long. Vaska, where there are many isolated weighted down at intervals with sinkpinnacle rocks and ledges under water, ers and supported at any desired depılı or along shores like those of Florida, by surface buoys. Several power-boats l'orto Rico, and the Philippines, where are hitched to it, usually one at each end coral reefs abound and coral heads and one in the middle, and with these fringe the coast, special investigations it is drawn around a harbor much as c have to be made. The lead line migli farmer drives his linder around his field be cast

all around a pinnacle rock of standing wheat. If it strikes no obmight even strike it a giancing blow struction the hydrographers know that and still fail to discover it.

the harbor bottom is cicar to the deptii In instance of this kind occurred in of the drag (see page 656). Buzzard's law, llassachusetts, in 1902. Inother line of information the mari

Although more than 01,000 soundings ner must have is about the movement oi has been madde, more than 10,000 angles currents, so that his ship may not be

A PLANT-TABLI; SURVEYOR MAPPING SECTION OF SPIORI;-LINE In making a survey of a harbor or section of shore-line, it is necessary to prepare a topographic map of the surrounding territory, showing all objects in the landscape that will help the navigator to fix his position (see page 658).

carried around by currents whose pres ords, 7 volumes of altitude records, and ence he does not suspect. Information 8 volumes of magnetic records. concerning them is gathered by means Obviously the proposed chart cannot of current rods, as a rule. A current

be as big as the area it is to represent, rod is an instrument made to float verti

so the first thing to be determined is the cally beneath the water, with only its scale to which it is to be drawn. In reptip showing above the surface, so that

resenting a harbor the usual scale is apit is not disturbed by the wind. Its

proximately half a foot to the mile, or movement is observed, and the observa

exactly one foot to ten thousand feet. tions give definite information concern

For ordinary navigation along the shore, ing the currents.

where ships keep outside the 100-fathom

line, a foot on the chart may represent MIKING TIME CILIRT

nearly So miles, or, to be exact, 400,000 IVhen all the work in the field has feet. On charts used to approach the been finished, including observations coast the usual scale is about a foot to which show the deflection of the mag 16 miles, or one foot to 80,000, to be exnetic needle, the force goes back to head

act again. In all cases a foot on the quarters and begins the task of "writing chart represents just as great a distance up” its notes. And a bunch of notes on the land or on the water as a clear they are to be written up! To make it exposition of the facts to be placed on single chart of a single harbor may re the chart will permit. quire as many as 12 sheets of field After the map is drawn it is reprohydrographie drawings, 16 sheets of duced either on copper plates or on alumifield topographic drawings, 57 volumes num plates. By photography a copy is of soundings, 22 volumes of tidal rec made from the drawing, and this is laid ords, 20 volumes of trigonometric rec down on the copper to fit the latitude and

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MASTRLIG I 1.1ST:-1,LVE In all Coast and Geodetic Surer work the accurately fixed and measured base-line is the foundation 11pon which everything else rests. It is measured by the use of invar tapes, which are almost wholly umaliccted by heat or cold. The tape is streicher under a uniform tension, lience the spring balance in the picture. The marks for each tapc-length are made in hardwood posts firmly set in the ground (see page 665).

OUR GUARDIANS ON THE DEEP

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longitude marks. The impression is then nished to all the ships of the American chemically fixed on the plate, and the navy, and the chart-room of one of the engraver, who must have a high degree big superdreadnoughts contains a series of skill and accuracy, proceeds to work. of cabinets where the charts are alway's The figures showing the depth of the kept, ready for reference at a moment's water at each point are put on the plates notice. The Hydrographic Office furby a machine, one man being able to do nishes the same kind of charts for forwith the machine the work of several by eign coasts that the Coast and Geodetic hand, cutting uniform figures and putting Survey furnishes for home coasts. them in with mechanical accuracy.

Nearly a thousand different charts Printing from copper plates is á labori have been prepared of the coasts of the ouis process. The ink is first placed on United States and its outlying possesthe plate and then wiped off with the sions since the Coast Survey was organpalms of the hands of the operator and ized. These range in importance from his assistant, leaving only a tiny bit ad the great charts of New York harbor, hering in the engraved lines. It is then where billions of dollars worth of comrun through the press, in contact with merce and millions of lives are safewetted paper, after which the prints are guarded every year, to the charts of calendered by being subjected to a pres places in Ilaska, where a ship may not sure of 600 tons in a hydraulic press. be seen more than once a week, or even

For cheaper and more rapid work once a month. The charts are in great aluminum plates, coupled with the litho demand by navigators at home and graphic process, are used. A drawing is abroad, and the annual sale amounts to made on tracing vellum and then photo more than a hundred thousand copies. graphed on a sensitized glass plate. Positive plates are made from these negatives,

ASTONISIIING PRECISION and from these are transferred to the The geodetic work of the Coast and aluminum plates, which have been sub Geodetic Survey forms a fascinating stituted for stones in the lithographic part of its activities when one looks beprocess. One of the old stones weighed hind the mathematics involved. It deals 640 pounds and cost $185; the aluminum with conditions that very many people plates weigh 5 pounds and cost $4.50. do not know exist, and requires measure

All the original information upon ments of a refinement that must elimiwhich every chart is made is filed away, nate even the personal equation. and if one little detail were found wrong When work must be so accurate that 10 vears later the very man who made it requires the elimination of the differthe error could be located.

ence of the speed with which the eye

telegraphs to the brain and the brain to 100,000 CILIRTS TRE DISTRIBUTED EACH

the hand, in two men ; when it must be

so exact that a line a mile long may turn The vast importance of the hydro to the one hand or to the other no more graphic work of the Coast and Geodetic than 1/33 of an inch ; when it must reach Survey is illustrated by insurance rates that standard when the average error is in harbors where it has done its work and less than one inch in 500 miles in levelin those in which it has done nothing. ing work, it is apparent that the most In Nome, Alaska, for instance, the ma delicate instruments and the most refined rine insurance rate is five-eighths of one measurements are required. Yet such is per cent, the harbor being surveyed. At the standard set by the Coast and GeoKuskokwin, Alaska, the rate is from 1 1/2 detic Survey for its finest surveys. per cent to 5 per cent, with the agents It determines the longitude of a place not eager for business even at such rates. br

a transit instrument and the The charts of the Survey are kept on telegraph—the transit instrument showsale at all times, and are sold at a price ing to 1/500 of a second the exact mowhich covers only the cost of the paper ment at which certain stars cross the and the actual printing. They are fur meridian of the place, and the telegraph

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.I TRLLICITATION STATION When doing triangulation work in a level or wooded country; it is sometimes necessary 10 build a high lower that will bring the observers above the trees and buildings of the neighborhood and afford then un uolstructed view of other towers or natural objects in the distant landscape. On the coast of Washington a crow's-nest was built on a tree-top und an elevation of 215 Icet was secured.

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