contended that so long as a marine survey was graphically correct very little attention need be paid to topographical details. Before the war the delineation of topographical details was but a secondary consideration in a hydrographical survey, and it was limited to the accurate fixing of objects conspicuous from seaward; contouring, except in large harbour plans, was generally sketched in by form lines. The experiences in the World War showed that in localities of possible strategic value accurate topography is of great importance. Where no land sur- veys are in existence or contemplated, the delineation of the land features must be included in the hydrographical survey. The lack of information due to the neglect of this important subject was much felt during certain operations of the war, particularly as affecting long range naval bombardments. The necessity for this accurate work on the part of the hydrographic surveyor has resulted in the adoption of new methods and of new instru- ments and the more general use of the land surveyor's instru- ments, all of which undoubtedly tends towards the more accurate charting of the seas. The elaborate methods and rigid accuracy of a triangulation on shore have been recognized by marine surveyors, although the refinement necessary for so-called first- class triangulation work does not often present itself.
Instruments. Theodolites in current use (1921) are 4 in., 5 in. and 6 inch. The majority of these, formerly graduated to one minute, read to 20 sec. by Vernier, and micrometer theodolites read to 10 seconds. The use of the theodolite for astronomical and tache- ometer work largely increased. Sextants for observing, with stand and artificial horizon, continue in use, but improvements in the sextant such as an endless tangent screw and electric light for night work have been adopted. More portable folding stands with slow- motion screws for movement of the sextant in azimuth and altitude are also supplied, and in addition amalgamated troughs, consisting of gold-covered plates on which a thin film of mercury is floated! have superseded the old artificial horizon consisting of a mercury bath ; the new pattern is far less sensitive to earth tremors caused by surf, traffic, etc.
The Astrolabe a Prisme, a very precise instrument for finding posi- tion, enables altitudes of any stars at the exact altitude of 60 to be observed (see John Ball and H. Knox Shaw, A Handbook of the Prismatic Astrolabe, published by the Egyptian Government, Cairo Government Press, 1919).
Measuring chains have been almost entirely superseded by loo-ft. and 500-ft. steel measuring tapes, which are supplied with standard- ization certificates. The " lo-ft. pole" has been supplemented by a " 20-ft. pole " operated by two men and consisting of two boards connected by a wire 20 ft. in length and used in conjunction with a sextant. This method of measuring distance is, however, being gradually superseded by the use of tacheometers and tacheometer staves marked according to the Admiralty pattern, with which dis- tances up to over 2,000 ft. can be very accurately measured.
One-metre base range-finders are useful in measuring short bases for plans of harbours, etc., when time or circumstances do not permit of a more accurate method.
Of the various forms of heliostat the Gallon sun signal has proved a most excellent instrument, and fitted to theodolites it allows of the sun's rays being expeditiously and accurately directed to, and kept on, the station desired, whether the latter is visible or not.
Ship sounding has been greatly improved by the introduction of the Douglas Schafer sounding gear, which enables ship sounding to be carried out under way in any depth up to about 40 fathoms with great speed; other methods of sounding such as the " Somerville " gear have also been adopted, and. in addition, far greater attention has been paid to sweeping for rocks, shoals, etc., the method used for mine-sweepin? having been adapted to thh purpose.
Other entirely different methods of sounding were also due to experience gained during the war. The most popular method under trial in 1921 was " Acoustic Depth Sounding " which depends on- the principle of the acoustic echo, the depth being measured by the time taken for the shock of an explosion or other impulse produced in a ship to reach the bottom and be reflected back as an echo to a receiver on board the ship. By this device it was hoped to obtain either a single indication of the exact depth at any moment or a con- tinuous indication of the depth registered automatically at any selected position. The importance of this method of sounding from a ship under way at any speed, without the necessity of casting the lead, needs no insisting upon.
Taut wire measuring gear was in 1921 fitted or being fitted to all British surveying ships. This method of measuring distances at sea in comparatively shallow depths had proved most successful and was adopted after having been extensively used in connexion with mine-laying during the war. The ship preserves a steady course and at a constant speed over the distance to be measured and at the same time runs out a thin piano wire from a drum which carries many miles of the wire. It is laid taut by means of a special brake
device, the amount of wire out being registered on a dial. A correc tion (always subtractive) must be made for errors. This varies trom 1,000 to 3,000 ft. in a distance of loo m., and is governed bv the contours of the sea bed upon which the wire has been laid The dial registers 1 ,000 rev. for a mile of 6,080 ft., consequently when plottine in sea miles a second correction, for latitude, is necessary. This method of determining distance is specially useful when surveying out of sight of land, and is used in combination with astronomical observations and moored beacons.
Fixing Positions of Ships, Buoys, etc., by Subaqueous Sound- ranging. This new method of accurately fixing the positions of buoys, etc., is carried out by dropping an explosive charge at the position it is required to fix. The sound of the explosion travels hroughthewatertoa number of hydrophones suitably placed and the positions of which are accurately known. The differences between the times at which the shock reaches the various hydrophones are
- orded photographically by a galvanometer on shore, to which the
instruments are connected by cables. From these observations it ig possible to calculate a position line for each pair of hydrophones i hree or tour such lines from hydrophones suitably placed will eive a cut, which is the position of the explosion.
As in all surveying problems, the accurate fixing of a point from two others depends on the length of the base, that is, the distance between two known points, so does the accurate fixing by sound through the water depend on the hydrophones, or groups of hydro- phones being such a distance apart, commensurate with the distance at which it is required to fix the buoy, etc."
Chronometers. Surveying ships are now supplied with from 8 to 12 chronometers of the box type, with pocket chronometers for use side the chronometer room. The chronometers supplied are selected instruments which have successfully passed most exhaustive tests at the Royal Observatory, Greenwich. For astronomical work on shore, the portable Lindqvir>t chronograph is employed In this instrument, a chronometer fitted with special contact pieces auto- matically sends an electric current every two seconds through an electro-magnetic coil, and thus, by suitable mechanism records every alternate second as a perforation on a paper tape, which is kept moving at a uniform rate by means of clockwork. The closing of a switch by the observer operates a second coil, which records the instant of observation in a similar manner by making an addi- tional perforation in the tape.
Wireless Telegraphy for accurate time and obtaining meridian distances has been adopted, and in this connexion the wireless Vernier time signals made by Eiffel Tower may be mentioned.
Amongst minor improvements introduced in surveying appliances since 1910 may be mentioned the standardization of the markings of leadlines, improved buoys for beacon work, light filters for fitting to the eyepieces of sextant and theodolite telescopes. _ By 1921, platinised and stainless steel mirrors for sextants and sun signals were under trial; electrical lighting arrangements to sextants and theodolites; eye shields for use in observing to assist in perfect orientation of the head; sextant supports to facilitate observations at sea; the arcless sextant which enables angles to be taken and rend off (on a drum) without the necessity of removing the eye from the telescope; wireless telegraphy outfits for use of detached parties, and the gyro compass, were all in various stages of experimental development. The Pillsbury current meter was entirely superseded by the Ekman current meter, and other meters such as the Daisy and Gurley were in use.
In calculating triangulations considerable time is saved in correct- ing for false station by use of the station corrector diagram, by which the correction can be obtained very quickly to any accuracy re- quired (generally about 5 sec. of arc) and the tedious trigonometrical calculation avoided. The slide rule has come far more into prom- inence for small rough calculations. As the result of modern in- ventions, it has been found necessary in recent years to produce special charts for the use of submarines and for other purposes in addition to the ordinary navigational chart. Charts for submarines indicate graphically the nature of the sea bottom, so as to indicate where vessels can rest with safety.
The introduction of wireless direction-finding stations as an aid to navigation has necessitated the production of charts drawn on the gnomonic projection, by the use of which positions can be more accurately determined. Additional charts are also required for testing range-finders and compass adjusting. Physical charts in- dicate the direction of prevailing winds and ocean surface currents at different periods of the year, localities and time where ice may be fallen in with, and the direction and force of the stream and drift currents of the oceans.
Considerable gain in accuracy has been obtained by printing charts directly on backed paper, whereby the distortion incidental to the old system of subsequently mounting them is largely elim- inated. (H. p. D.)
SUTTNER, BERTHA, BARONESS VON (1843-1914), Austrian
writer (see 26.171), who in 1911 became a member of the advisory council of the Carnegie Peace Foundation, died at Vienna June 21 1914.
See H. v. der Mandere, Bertha Suttner (1909).
