On the state of the surveys in Tasmania

(1)

145

H.

pictilis, Tate;

H.

Stanleyensis, Petterd; BulimusBufresni, Leach; andB. Tasmanicus, Pfr.

The

last mentionedspecies

was foundinabundance

upon

the leaves of Xerotes longifolia,

where, no doubt,

among

the roots the living specimens of

Pupa

Lincolnensis

may

be found.

The name

P. Tasmanica,

first given tothe shell, hasbeen withdrawn,as on comparison withAngas' P.Lincolnensis,kindly given

me

byMr.Petterd, IfoundthattheTasmauian form

was

not specifically distinct

from it.

Hithertoconchologistswereofopinion that thegenus

Fupa

had

no representatives in Tasmania.

The

discoveryofthefirst

representative will,therefore, beof

more

than usual interest to local naturalists.

Hobart,

December

12, 1881.

ON THE

STATE

OF

THE SURVEYS

IN

TASMANIA.

By

G.

McIntyre,

Authorisedand Licensed Surveyor, Christchurch,

New

Zealand.

[Bead9th

May,

1882.]

At

recent meetingsof the Royal Society thequestionofthe present state of thesurveysinTasmania

and

the best

methods

to beadoptedfor placing

them upon

asound basis was under

discussion,andvarious suggestions were

made

onthe subject. Subsequently, on the 27th October, a letter waspublished in The Mercury undertheheading "Field Surveyors," which

was

intendedas areply totheunfavourable

comments

which

had

been

made

upon theexistingsurvey system. This letter

was

signedby Mr. J. E. Calder,a gentleman

who

for severalyears held the ofiiceof Surveyor-GeneralforTasmania,andis there-fore entitled toconsideration asdealing with a subject with whichitis onlyreasonable to assume he is well acquainted. Statements, however, are

made

and reasoningsadopted which areopen tocriticism; while the general impression conveyed

tothe

mind

of the unprofessional reader

amounts

to this: That the surveysof Tasmania areasgoodasitis possible to

make

them

ina timbered and rugged country, and that a trigonometricalsurvey ispractically useless.

A

systemof surveyforalargeextent of country cannot be considered as inany degree accurate or reliable,unless it is

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146

even underthemostfavourable circumstances,totheMagnetic Meridian. Itis obvious thatanunalterablemeridiantowhich allbearings are referred, is, in itself, and apart from any

triangulation, of very great value; and when, inaddition, the

sectional surveys are connected with the stations of a

trigonometrical survey, whose relative positions have been accurately determined, a

means

is afforded by which the boundaries of such sections can be re-established in case of dispute orof obliteration.

Such

a systemis in force in

New

Zealand andin

some

ofthe othercolonies

—

Victoriaand

West

Australia,forexample.

An

accurate triangulationisrecognised as anessential

and

indispensable basis.

With

this

triangula-tion, sectional surveys are connected, andthe position ofeach peg is tabulated relatively to

some

trigonometrical station.

The

limit of errorallowedfor minortriangulationistwolinks in themile,

and

for sectional

work

eight linksin the mile,the great majority of the surveys executedunderthissystembeing actually

much

within the limit.

The

true meridian for each meridianalcircuit, and which governs the triangulations, is

observedasthe astronomical stationof thecircuit.

Under

a correct minor triangulation, the accumulation of errors

in-separablefroma system of

mere

traverse surveys built

up

the one

upon

the other, and which in a large extent of country

must

be very considerable, even where the traverse surveys are carefullyexecuted, is avoided, and theerror is not carried forward, butisconfined to the country between the trigono-metricalstations.

The

actual error in anycircuittraverse, or in a traversefrom one trigonometrical station to another, is

easily computable bythe solution of a series of right-angled triangles,each traverseline being the hypotenuse,

and

the bearing supplying the angle.

The

systemin force in Tasmania, lookedat from any point of view,

must

be regarded asextremelyfaulty,inasmuchas:

—

(1.) Itisnot based

upon

triangulation.

(2.)

The

sectionalsurveys are built

up

one

upon

the other, across largeareasof country.

(3.)

The

surveysarenotsubject toany mathematicalcheck, suchasisafforded bya reduction of the traverses to their co-ordinatesonthe meridianandperpendicular.

(4.) There isno systematic fieldinspection.

(5.)

The

limit of error allowedis so great as to preclude anything like accuracy ; the confusion and discrepancies

arising fromthis sourcealonerendering it impossible to re-establishboundaries, even where an admitted starting point

is available, within

more

than arough approximation.

(3)

145^

blocks, and withwhich toconnect the various town surveys requiredfrom timetotime under the RealProperty Act.

(7.)

The

surveys are

made

to independent magnetic meridians, the bearingsof the initial lineineach survey being derivedfromthe compass orneedle-reading.

(8.)

The

office plans and compilations are constructed entirely

upon

the "building-up" _system, _withoutthe check affordedby the connection ofsurveys with accurately

deter-mined

trigonometricalstations.

With

regardto sub-section (7) above, it is perhaps right to note that an independent or isolated survey, executed under the

method

therein indicated,

may

be extremely accurate in

itself, thatis withinits

own

boundaries; butitisobvious that the surveys, effectedby a

number

of surveyors, working to their

own

independent compassmeridians, which, even apart fromspeciallocalattraction, are certain tovary considerably

—

cannot be properly compared as toboundaries

and

relative positions,andare therefore " floating " to anextentwhichis

unknown

andpractically unlimited.

With

respect to sub-section (5),it is not unreasonable to

assume that where a certain limit of error is recognised, a considerable proportion of the surveys, especially in rough country, will

come

nearly

up

to thatlimit.

The

limit of error formerly allowedin Tasmania, andprobably still recognised,

was 32links inthe mile (1 in 250),a limitthree times greater thanafair allowance.

A

limitof error of 8 links in the mile

(1 in 1,000) forordinary sectional work, is regarded as a

maximum

allowance under any system professing to give reasonably accurate results.

The

statements

made

by Mr. Calder in the letter above

referredto,

may

be fairly summarisedas follows:

1. ThatTasmaniais so densely

wooded

and rugged thatit isimpossible to adopt a really accurate

and

scientific system ofsurvey, and its peculiarities "will foreverenforce peculiar

modes

ofsurveying."

2. That thesettingasideofthecompassmeridian in favour oftheTrue Meridianwould, onaccount of obstructions,involve a " delay of severalhours aday inthefrequent determination oftheTrueMeridian,whichwould be requiredofthe surveyor, in

many

districts, every time theboundaryline ranintoa tree too massive to beremoved."

3. That " trees are notto be passedby withoutliabilityto error;"

and

thathehasfoundin practiceno " better

method

ofmastering the difficultythanthat ofobserving thecompass bearing of the line at the point of obstruction, and then proceeding inthe

same

directionfrom its opposite side.

By

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148

prettyoftenrepeatedina day'swork,willgenerally not exceed half-a-dozen yardsina mile."

4. Thatthe greaterrors existing inthe

maps

are really errors of compilationintheoffice,andnoterrors ofsurveyinthefield. 5.

That

it isnot desirable to undertakethe reconstruction of the maps.

6.

That

the trigonometrical survey executed

many

years ago

was

a fraud,

and

entirely unreliable.

7.

That

"inthedaysof fieldsurvey inspection" the

work

of nineteen-twentiethsof the surveyors "stood the severest teststhat could be applied toit."

It willbeconvenientto consider these pointsseriatim.

1. Densely-wooded and rugged country.

—

It is better to

show what

has been done in othercountries, thanto advance

mere

theories;

and

it canbeproved that these obstaclesare

by

no

means

insuperable. In

New

Zealand there is to be foundasdensely-

wooded and

ruggedterritoryasany thathas everbeensurveyedin Tasmania, and yetit isfoundpracticable toapply anaccurate system throughout. Extracts fromthe

Annual

Reports (1880) of

some

of thechief surveyors will

furnish evidencein supportof this statement.

The

Chief Surveyor for

Auckland

district says:

—

_"

We

havein

hand

at thistime 23,000acres,all ofwhichis situated in the most broken, mountainous, and difficult part of this island."

The work

of

some

of the surveyorsis "situated in thedensely-wooded and precipitous mountains of the East Cape.

...

I wish to state

my

opinion, based ona_3| years' trial, that the systemof survey . . . has been found

to

work

as well in our forest- clad, broken country of the north, as inthe openplains ofthe south."

IntheWellington districtthesectional surveys,

amounting

to over 93,000acres, are stated tobe "allunderforest."

The

Chief Surveyorfor Nelson speaks of the country, in

whicha largepartofthe surveysduringthe yearweresituate,

as

"

rugged,mountainous,heavily-timbered, with dense under-growth,"

and

adds, "_the_bulk_{of applications to}_be surveyed are in isolated sections, orin smallgroups

...

in

many

casesonly accessibleby rough bush packtracks

Mining

surveysin severallocalities are 3,000ft.

and

4,000ft.

abovesea-level,

and

generallyinbushonruggedmountainsides." Eeferring toa portionof the triangulation in Otago, the chiefsurveyorforthatdistrictsays,

"This work

is spread over 30miles of wildAlpinecountry, fullof bush,

and

intersected by dangerous snow-fedrivers."

Of

thesurveysin Southland, the report states that "50

(5)

149

Enough

has been quoted to dispose of the first point ad-vanced by Mr.Calder.

2 and3.

Bush

lines and meridian.

—

One

would be led to

infer, fromthe statements made, that the prismatic compass, orthe compass attachedto the theodolite, afforded the only available

method

of obtaining the bearings or azimuths of

lines,whereasitought tobe taken forgranted, as a matterof course, thateven inthe case of a survey,basedupon an

inde-pendent magneticmeridian, theinitial line of the survey

was

the only one observed by the compass, the bearing thus obtained beingtransferred to the plate, and all subsequent readings derived therefrom.

To

whatever meridian the

work

is done,orfrom whatever source derived,whether compassor astronomical,the veriest tyro

must

be awarethat thebearings are carriedon bythetheodolite,andthat the proofofaccuracy

is found in the extent of accordance in the closure, either

upon

one of thelines ofthe survey in hand, or at a trigono-metrical station.

The

argument advanced has therefore no foundation either in theory or in practice. If it has been

inany degree thepractice to

make

surveys by compass only,

itoughttobeno matter for surprise if the discrepancies in the various surveysarefoundtobestartling. Stilllessshould thosediscrepanciesbe a matter forsurprise

when we

have an

authoritative assurance that themost favourableresults have beenobtainedfrom such a processas runningaline by com-pass bearingto some large tree, and then, after transferring theinstrument byguessto asupposedcorresponding pointon the otherside,carrying onthelineagain bycompassbearing and thisnot onlyin anisolated case, but"adozen ortwenty timesin everymile." Itisalsourgedthatbythemysterious correction of "compensation" the error "will generally not exceed half-a-dozen yards in the mile." Admittedly,

there-fore,the error

may

in somecases be

much

greater; buteven

what

is considered a favourable instance depends entirely

upon

chanceor luck.

The

errors,it is said, compensate each otherto a great extent; butitneeds hardlytobe stated that

theerrors

may

beallthe one

way

—

allinthe

same

direction

andthen insteadof thecompensation of errors bringing the neterror

down

to "half-a-dozen yards inthe mile," the error

may

be increasedindefinitely.

4 and 5. Errors inmaps.

—

The

statements

made

underthis

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150

satisfactorybasis, concurrentlywith orsubsequenttothefield

determination of thetrue relative positions of a

number

of pointsinthe severaldistricts.

6.

Former

triangulation useless.

—

This assertion, even if

established, in no

way

detracts from the advantages of a trigonometrical survey honestly done,and reliable asa basis of detail operations.

Nor

is there anything in thenatureof such a surveyto

make

ita matterofuncertaintyor speculation. If funds are forthcoming, the result ought not to be pro-blematical.

7. Fieldinspection.

—

It would beinteresting tolearn

what

extent of surveys were rejected or

condemned

" in the daysoffieldinspection."

As

the "severest tests"recognised a limit of error of 32 links in the mile,the standard of accuracycanhardlybe considered high.

To

keepwithin the limit specifiedwas one of the conditions of each surveyor's work,

and

it is obvious, therefore, that only those surveys which were found on traverse inspection to exceed this limit couldbe condemned. But, further, as there

was

no triangu-lation by which to test the surveys on inspection,the

in-spector's

own

work

would have to be discountedsomewhat,

and

allowing thatofficer alimit of error of 8 or 10 links in the mile, asitwouldonly be a traverse inspection,it is not beyond thebounds of possibility to assume that he might pass

work

whichwas erroneous to the extent of something like40 links inthe mile, or4in.ineverychain.

Apart from general considerations as to the

wisdom and

propriety of establishing an accurate system of survey, the

factthatunderthe Real Property Act titles are issued for certain pieces oflands,the boundarieswhereof aredefined in thecertificates

and

guaranteed, renders itnot only desirable

but essentialthat the

methods

ofsurveyandofrecord should be such as to effectually guard against overlaps of boundaries and consequent futureclaims