1000062609_037

IN'fERNATIONAL AMERICAN CON:E'ERENCE.

173

In Russia, the military topographical corps is charged with surveys. Its organ–

ization is :

genera

lo; 3:3

majors, lieutenant-colonels, and colonels;

150

c01;nets, lieu–

tenants, and cap.tains ;

170

classed topographers; 236 topographers, of sergeaut's

rank; 42 apprentLCcs.

The main divisions of the work of a European state survey are usually three, the

trian.,.ulation, the topograpby, aud the cha1·tograpby. When it is practicable, the tri–

angulatiou precedes the topograpby, and includes the primary, secondary, aud ter–

tiary trian<Yulatiom; and their computations.

the trlangulatiou points thus determined are numerons, as in the Prussian snr–

vey., additional triaugulation by

t.be

topographer will 11ot be needed; when, as in

L\.n

·tria, comparatively few points are determiued, the topograpber will have to base

on tbem a smaller triangulation for his detailed 'York.

Tbetopographers baviug been furnisbed '"ith the positious of certain points within

the area to be covered by one of tbeir topographical sheets, make a survey of that

area, whose amount of detail will depend on tbe scale or object of the survey. Their

work includes the determination of tho required level-curves.

The topogrn.phers' sheets go to the chartograpbic diYision, whence they are either

reproduced ou tbe same scale or reduced to a srualler scale, and the maps resulting

from

them ·are pnblished.

METHODS.

is only within the present century that t h e methods of geodetic

anrl

topograpbic

surveying for large areas have reached high precisioq. Previouslythechiefspurto

the prodnction of accurate maps was their necessity for military purposes. In sorne

states progress beyond this need has scarcely boen made as yet, and the maps give no

more detail than ís needed for the movement of troops; in others, and notably in

Great Britain and Germany, the progresa in civilization, thc needs of the govern –

ment, and tbe dense popul:1tion, have required and have obtamed the adoption of

systems of topographical survey and publication, 'vhich are sufficient for all rational

demands.

A.side from the military uses of maps, uses that in Europe must long be amoug the

most important, the iucreasing intelligence of man in civilized con utries demanda

~1n

a.ccnrate knowledge of tbo eartb's surfaee in bis viciuity; a surface that, while

lightly modified. by his acti· n upon it, yet reta,ins the same principal feature from

~ge

age, so tbat one good snrvey, with slight occasional corrections, will

su.ff

:ice

for an indefinite period.

Where the survey is on a large scale it serves auother pnrpose, by giving, with

sufficient accuracy for the imposition

ofta:x.es,

the a reas of all estates, and may, in–

deed, be

ma.de

a basis for land titles. This, however, requires a larger scale than is

necessary for ordinary purposes. In England, such maps, called parisb plaus, are

on a scale of

~·

In many European states, cadastral surveys have been macle fre–

quently without connection witb a topographical survey, their object being the

proper apporVionment of land-taxes.

A.gain, when an accurate survey of a country is made, it wi1l aid in the prelimi–

nary examinations for works of engiueering, sucb as railroads, canals, river improve–

~ents,

although no general survey could properly give the

deta.il

necessary for the

finallocation or construction of such works.

In nearly all the Europeau states the area over which the survey extends is covered

a net or chains of triaugles of large size, tbe lengths of whose sides vary from

lOO

miles, and depend on bases measured with the bighest precision that it is prac–

ticable to reach; their probable errors not e:x.ceeding about

auo~

part of their lengtbs.

In sorne states all the angles of this n et are observed witb extreme precision, so that

th~

probable error of any angle sball not exceed a few tenths of a second ; in others,

as m Italy

a.nd

Spain, certain cbains of triangles,

100

200

miles apart, running north

and south and east and we8t, thus forming 1arge

qnadrilaterá.ls

, are observed with

the greatest precision, the intermediate triangles receiving less care. At the vertices

of several of the triangles accurate determinations of la.titude aud longitude are made,

a.nd

the azi.mnth of a triangle side

determined. 'fhe heights of t he gronnd above

the

lev~l

the sea at all vertices are found either by levelings of precision, or trigo–

fom~trically.

'fhe positions of these vertices are tbns accurately known in latitude,

fion~1tude,

and e1evation; they are the p recise reference points on which all the

in–

enor points depend.

Sta~ng

from the triangle sides of the primary triangulation, tbe interior of each

such tnangle is cut up into a smaller triangulation, called secondary, and the sec–

~dary ~ria.ngles,

ifnecessa.ry

, into stillsmaller ones, called tertiary. The v ertices of

b e

ter~aary

triangulation are the guiding points of the topographer; on them he

asea bis sbeets.

::r'hn , in Austria two or three such points at least are required for every sheet cov–

enng 7t minutes of latitnde and 15 of longitude, on a scf\le of

muo-,

with one or two