Thursday, 21 January 2010

James McKerrow's Geodetical Surveys

I have had a few people asking me about James Mckerrow's work on Geodetical Surveys. here is a page from David Herron's 1948 Thesis.

GEODETICAL SURVEY
IN his annual report for 1862, Mr.J.T. Thomson made a recommendation that McKerrow be employed on Geodetical 1 operations after he had completed the Reconnaissance surveys. Under Thomson’s tutelage he would gain practice in this type of operation 2, so that unaided, he might establish standard bearings and distance, and set up marks to guide the district surveyors 3.As long as the detailed surveys were confined to narrow limits, no harm could arise from the use of small instruments in directing general survey, but as operations were extended the governing power of larger and more delicate appliances became more and more necessary. The cheap and rapid Reconnaissance surveys were adequate to control all preliminary arrangementsfor settlement and to guard against the possibility of major boundary disputes, but as minor triangulation and section survey extended slowly westward, the approximate observations of the Reconnaissance surveys were found to be palpably insufficient. 4Thomson had long been considering the advisability of securing a set of observations exact enough to maintain accuracy in succeeding surveys, but before 1864 could find neither the time nor means to do so.

It had been intended to use the department’s solitary eightinch theodolite to carry out major triangulation from the series of bases sixty miles long. This scheme would have taken twentyeight years to complete5, but the discovery of gold however,
and the subsequent influx of settlers gave such an impetus to settlement in scattered and isolated communities that a more rapid system was needed 6

Thomson had two courses open to him. One was to carryout operations in areas unconnected with one another; the other to use a common standard of reference connected with given points. A decision was essential; to temporize would have
meant immediate relief, but ultimate disgrace and disaster 7
Thomson knew only too well that when isolated and unconforming surveys close, confusion and overlapping is inevitable, and it comes as no surprise to learn that he decided on a system governed by common references. Throwing time-honoured precedents to the winds, he adopted a system appropriate to circumstances. It had as its bases the use ofmeridional circuits; it was rapid, would control settlement
survey and did not deviate from true principle 8. What more could be desired?
The province was to be divided into five large districts named meridional circuits. These were to be not more than 120 miles in length and 90 in breadth, and were to be bounded by conspicuous geographical features. In each circuit there would be set up an initial station, central if possible, from which observations for latitude and true meridian would be made with the eight-inch transit theodolite. 9 The methods to be used were those of “equal altitude of stars”, and “high and low stars”. From the initial points bearings would be extended and traverses carried firstly down those valleys already inhabited, and ultimately into every accessible corner of the province.

Points on these traverses, called geodetic stations, would be placed from ten to fifteen miles apart, and bearings of the traverse lines, all referring to the meridian of the initial station would become fundamental bearings for all subsequent minor triangulation and section survey.10

McKerrow spent his first season in geodetic surveying in extending true bearings in south-eastern Otago.11 His theodolitewas set up at Trig. Station A., North Taieri, the initial station for the south-eastern districts, and from that point observationswere taken to find true meridian 12. The first set of observations taken were to discover the altitude and azimuth of the sun13,
but it was found that evaporation from a nearby swamp was having a considerable effect on the readings. To obtain results independent of this error, observations were directed to thestar B Orionis (Rigel) in order to apply a system of calculation
known as equal altitudes and azimutha 14. This method relied for
success on a clear sky for several hours, but being independent
of latitude, time and altitude, reduced the possibility of error to
a minimum, provided that the instrument was not disturbed.
Reference before and after observations to a distant mark
precluded the possibility of a disturbance passing unnoticed.
The same method was used to determine the true meridian of
Observation Point, Port Chalmers, although on this occasion,
a different star was employed.

The latitudes of the stations were found by observing
stars north and south of the zenith. The stars selected did not
differ much in altitude15 or right ascension 16; thus errors due
to refraction affected each star equally and were neutralized.
It was important however, that the instrument be adjusted
perfectly horizontally. It it wasn’t when it was turned round
to the second of the two stars any error would be doubled.
To guard against such a contingency great care was taken in
levelling the horizontal limb, and, as an added precaution, the
instrument was placed on a massive stone pedestal and wellprotected
from the weather.
McKerrow considered that the mountain masses close to
the initial stations might also be suspect if errors crept into his
observations. To check up on this possibility he recommended
the comparison of measurements by standard chain and
latitudinal observations on half a mile of meridional line on a
level plain. Such an experiment would show the accuracy of the
theodolite observations and enable corrections to be applied to
the initial point.
At Port Chalmers the observations for latitude were taken on
still clear nights, and the results compared with those obtained
by Captain Stokes of the Acheron and by Mr. Thomson. Cloudy
weather hindered operations at North Taieri, and appeared to
preclude the possibility of anything other than an ordinary
geographical determination. McKerrow decided to leave a
geodetical determination for some other time, however, and as
soon as he had determined true meridian began the extension
of bearings through south-east Otago so as to overtake the
surveys in progress. Within a few months bearings on true
meridian had been extended through the surveyed districts
in Kuriwao Peak17 and thence to Glenomaru18, Waikawa19,
Tuturau20, Toitois21 and to the Pomahaka22 and Waikaia valleys.
From Port Chalmers bearings were extended to Black Hill and
up the Waitaki Valley and a start made up the Shag Valley
One of the stations of the minor triangulation was always
converted into a geodetical station if the district had been
triangulated, and from it a round of angles were taken to the
surrounding stations. In this manner much minor triangulation
was checked and the difference between it and the standard
system noted. In unsurveyed districts a reference trig station
was erected within two or three miles of the geodetical station.
This made the geodetical stations available for checking. The
stations were built of stones, when it was necessary to erect one
– otherwise a stone was placed in the centre of a circular plot of
ground twenty feet in diameter and enclosed by a trench. The
augur point was the centre of a circle carved on the face of the
block. Reference trig stations were always selected so that they
could be of use in the minor triangulation system.
To keep the theodolite safe during the journey from station
to station, its parts were placed in strong padded boxes and
carried in a spring wagon. Moreover it was screened from sun
and wind during observation, and its adjustments frequently
checked.
Another duty which fell to McKerrow during his time as
Geodetical Surveyor was to lay down standard length chains
for the use of district surveyors. During his first season he did
this at the Custom House Dunedin, at the survey offices in
Popotunca, Toko, Oamaru, and Hampden23, and on the rocks
on the Otago side of the Mataura Falls. Stone blocks with brass
centres were placed sixty-six feet apart in the ground while the
temperature was between 55o and 60o F. For the convenience
of surveyors testing chains, an oblong pivot was placed on one
of the brass plates, and on this one of the handles of the chain
could be hung while the other was brought up to the graduation
on the second plate. At each ix feet pegs were driven in, so that
if the chain rested on them while being tested, it would be in
one and the same plane.24 At the Mataura Falls the rock had to
be cut down to the level of the line joining the brass centres.25During the course of his work, McKerrow was frequently
called on to repair or renew stations of the minor triangulation.
In some cases both mound and trig were gone and it was
necessary to take observations to re-determine their position.26Mr. J.T. Thomson was gratified with the results achieved.
In his annual report for 1863-64 he stated that “particular
notice is called for to the most important operations that
have been undertaken since I had charge of the Department,
viz. the Geodetical Survey conducted by Mr. McKerrow . .
. So far much objection cannot be taken against the survey
as the error does not exceed the maximum allowed in lineal
measurements; but had the work proceeded on to more distant
areas the error would have increased so materially as to be a
cause of opprobrium against the survey, and this not only in a
professional point of view, but errors of sufficient magnitude to
cause lawsuits regarding disputed boundaries would have crept
in to so great a degree as probably to put the province to the
expenses of a revisal of survey.27On the recommendation of the Chief surveyor McKerrow
spent 1865 in carrying geodetical bearings further into the
interior28. Astronomical observations for latitude, true meridian,
and compass variation were taken at Lindis Peak; then standard
bearings were extended down the Ahuriri Valley to meet with
the line of bearings previously extended up the Waitaki Valley
from Observation Point Port Chalmers. Reference stations were
erected at various points, and standard chain lengths again laid
down, this time at Peninsula Pt., between Taieri Lake and the
mouth of the Kyeburn, at the Mining Survey Office Warden’s
camp, Clyde, and on the banks of the Clutha.29McKerrow’s work once more earned him the approbation
of Mr. Thomson. Regarding the cost of geodetical survey
operations (£114/7/3), the latter wrote: “I need say little, as
the high importance of the service to all future surveys of this
Province is now well established.”30One more season was required for the completion
of geodetical operations, and it was occupied in making
observations for latitude, true meridian and variation of
compass at Mt. York and Mt. Nicholas, and in re-determining
the latitude of the station at North Taieri. The observations for
latitude were taken under flawless conditions. On comparing
the two sets of readings for the latitude of North Taieri,
very little difference was found, a tribute to the accuracy of
McKerrow’s work. When the true meridians of Mt. York
and Mt. Nicholas had been determined, the bearings of the
different meridians were extended and closed on one another,
and it was possible to draw a comparison between calculated
and observed meridional differences.31
Only a slight discrepancy was found, despite the
incorporation of errors accumulated during the extension of
bearings through as many as thirty intermediate stations. A
further comparison, this time of the latitudes obtained during
the Reconnaissance Survey on one hand and the geodetical
operations on the other, led McKerrow to report that “it is
satisfactory . . . that the differences are so nearly uniform”.
Standard chain lengths were laid down during the season at Fern
Hill, Te Anau Downs, and at the Survey Office, Queenstown.
Mr. Thomson received the final report with enthusiasm32.
“The primary operations that will henceforth regulate and
govern all survey operations in the Province I am happy to
state have now been completed by Mr. McKerrow, in so far
as it is at present necessary, the strip of precipitous land on
the West Coast alone remaining, but which does not call for
survey . . . The total cost of the geodetical operations have,
from their commencement amounted to £3735.17. These
operations have extended over 10,300,000 acres, as the rate of
cost per acre is only 8/100ths of a penny . . . As these points
or stations are accessible to all surveyors in different parts of
the province wherever employed, they can now proceed with
their work correctly and without error or difference. A map of
these standards bearings is now in the course of publication so
that the benefit of Mr. McKerrow’s labours will be at the easy
command of all . . . I annex Mr. McKerrow’s report. On his
last year’s work in full, by which the care, patience and skill
with which he has pursued his labours, under many difficulties,
discouragements and not to mention perils, during these last
three years, will be apparent to the Government. The work as
it now stands, if it goes no further, will be a lasting monument
of his services to this department and I have no doubt will
be fully appreciated by those who will reap the most benefit,
viz. the members of his own profession, and the settlers whose
properties can now be surveyed without fear of errors and law
disputes”.
In a newly settled country such as New Zealand in the sixties,
there was opportunity for pioneer work in many spheres; work
of a permanent nature which when done is done for all time.
Thus McKerrow was fortunate in that he was able to secure
a standing in New Zealand surveying circles by engaging in
geographical work of peculiar interest to the colony. McKerrow
himself, with characteristic modesty, attributed his success
to his good fortune in being entrusted with the vital work33,
but the fact remains that he was picked from a staff of highly
competent craftsmen as the most suitable for the job, and he
carried it through to success. He overcame great hardships34,
D 106 d SURVEYOR, EXPLORER AND CIVIL SERVET
used his ingenuity to meet problems as they arose, and secured
valuable and exact data. The value of the Geodetical Surveys
can be established from this fact – they still form the basis of
Otago Surveys.
Notes
1. Geodetical survey, as opposed to plane survey, takes into account the
curvature of the earth. It ties the humbles village in with a world-wide
scheme. Geodesy means literally “earth division”.
2. Otago Prov. Gaz. Vol. V, November 26, 1862, p. 207.
3. V & P Otago Prov. Council, Session XVIII, 1863, Departmental
Reports, p. 12.
4. V & P Otago Prov. Council, Session XIX, 1864, Departmental Reports,
pp. 31-3.
5. Palmer, Major. State of Surveys in New Zealand, App. H of R 1875,
H1.
6. Thomson, J.T. Exposition of Processes and Results of the Otago Survey
System, p. 11, Pamphlet in Hocken Library.
7. V & P Otago Prov. Council Session XXVII, 1870, Departmental
Reports, pp. 30-33.
8. Ibid.
9. The theodolite is used to measure horizontal and vertical angles with
the aid of a telescope and graduated circles. Theodolites are grouped
into two classes; plain and transit. The latter is used for astronomical
and geodetical observations, and differs from the plain in one respect.
The telescope of a plain theodolite can move through an arc of about
45o upwards or downwards from the horizontal plains; in the transit
theodolite the telescope may take a complete revolution from the
horizontal. Thus a different method of mounting the telescope to
correct its adjustments is necessary.
10. Palmer, Major, op cit.
11. V. & P Otago Prov. Council, Session XIX, 1864, Departmental
Reports, pp. 4-8 [McKerrow’s Report].
12. True meridian as opposed to magnetic meridian.
13. The zenith is the point in the celestial sphere immediately above
the observer’s head. The angle which the plane passing through the
zenith and the heavenly body makes with the meridian is known as
the azimuth of the heavenly body. It is generally measured from the
James McKerrow D 107 d
north towards the right, and will of course vary from 0o to 360o. The
term is thus practically synonymous with bearing, and means merely
horizontal direction.
14. All stars appear to revolve from east to west around a point in the sky
known as the Celestial Pole. To mark out a true north and south line,
the direction of the celestial pole must be determined. The simplest
way to do this is to observe a circum polar star, wait until it is seen
again at the same altitude, and then to bisect the line adjoining the
two points of observation. The celestial meridian is thus obtained for it
starts at the celestial pole and passes through the zenith. True meridian
on the earth lies directly below the celestal meridian.
15. Altitude refers to the angular altitude of stars in a vertical plane above
the horizon.
16. Each star crosses a meridian at a definite sidereal time. The sidereal
time at which a star is on the meridian is called its Right Ascension.
17. About 70 miles south of Dunedin.
18. About 65 miles south of Dunedin on the Catlins Line.
19. On the South Coast of the South Island.
20. Forty miles north-east of Invercargill.
21. On the south coast.
22. Ninety-two miles south of Dunedin.
23. Popotunoa is near Clinton, Toko near Milton.
24. V & P. Otago Prov. Council, Session XIX, 1864, Departmental
Reports, pp. 4-8
25. Field Book No. 163, Dunedin Survey Office.
26. V & P. Otago Prov. Council, Session XIX, 1864. Departmental
Reports, Pp. 4-8.
27. Ibid. Thomson’s Report.
28. Ibid.
29. Otago. Prov. Gaz. Vol. IX, September 20, 1865, p. 201. McKerrow’s
Report.
30. Otago Prov. Gaz. Vol. X. September 5, 1866, pp. 172-3, Thomson’s
Report.
31. The difference found when meridional circuits meet is due to the fact
that the meridian of any point in a circuit is calculated as though it were
parallel to true meridian of the initial point of that circuit. Actually it is
not, as lines of meridians converge slightly. Thus a slight discrepancy is
found at the point where circuits meet.
32. Otago Prov. Gaz. Vol X, 5th Sept. 1866, pp. 172-3. Thomson’s
Report.
33. Kilmarnock Standard, September 12, 1903.
34. Unfortunately no narrative accounts of the 1863-66 journeys appear to
have been kept. One of the chainsmen on these journeys died several
years ago at a ripe old age. He is said to have told many tales of the
adventures the party experienced in the

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