SURVEY OF NEW ZEALAND

New Zealand Times, Volume LXXI, Issue 4304, 13 March 1901, Page 7

SURVEY OF NEW ZEALAND

SOME OF ITS DEFECTS. SUGGESTIONS BY HON. G. F. RICHARDSON. Tho merits and defects of the Ne’-v Zealand surveys as now practically applied were dealt with ia a paper contributed to the AVellington Philosophical Society at its meeting last night by Ihe Hon G. F. Richardson. Among the noticeable defects, ,Mr Richardson gave first place to the want of an absolute unit of measure foi tho colony. On this point he said “As all our standards disagree, it s obviciqs that nine out of the ten must he wrong, and that probably all ten are; also, that these discrepancies must introduce a constant error through all work based upon them, apart from the inherent error of the work itself. I have recently brought this matter under tho notice of tho Government, which will, I have no doubt, take stops to lay down a standard chain length for tho colony, with tho highest degree of accuracy obtainable, and once a standard is determined, its exact duplication, by means of instruments of precision, is comparatively simple. The best appliances we possess aro two Imperial standard yard measures, which do not agree with each other, but even if they had been reliable, wo have not tho requisite apparatus to enable us to utilise them. “It is clearly necessary to lay down a correct standard for the colony, and as New South Wales and Victoria each possess a standard chain laid down with extreme carei, I should propose to compare one with the other, and if the coincidences warranted it, to establish our standard of length from theirs. The crypt below the new Parliamentary Library would be very suitable for its permanent resting place. Tho Brisbane standard chain (1890) has been tested with that of Sydney (1899), and with the United States American standard (1891, and 1899), tho coincidences being within l-720th inch.

“The next stop should be to bring our triangulaticns into harmony with the standard, and consequently with each other. Official objection is sure to be raised to thus eliminating error, on the ground of confusion, but such an objection will not hold water —the confusion exists, and the differences arising through, its removal should nob exceed the official allowance of error, and can in no way interfere with or affect title. ‘Having overcome the difficulty of determining a unit of absolute length, the question would arise how best to bring all important measurements into terms with it, and to do this within fine limits of error, the only certain and economical plan is to give further effect to our survey system (already described) and carry out tho long postponed primary tnangalation. This can be done with marvellous precision,and yet at a smaller cost than would have been possible a few years ago. Alany things dontributo to this result, hut chiefly the modern methods of measuring base lines and the fact that the country is now opened and its topography completed. Looking to tho necessity for a primary triangulation for our own purposes, and to the wider interests of science, I should like to gee it carried out as a geodetic work of refinement, ■ and applied to the measurement of an arc of meridian.”

Air Richardson, in dealing further with tho ascertaining and elimination of the aggregation of errors, said: ’ “ The cost of a geodetic survey is not now' prohibitive, though it necessarily increases with the degree of accuracy demanded, but up to 1-lOthi inch error, per miler of base, and to V-in*h error per mile of the triangulation, the cost is moderate. The elaborate apparatus formerly used in tho measurement of primary bases by means of short rods or bars, is now discarded in favour of steel bands ranging* from 80 to 500 feet in length (the most favoured length being 300 feet) and by means of these, results varying from a probable error of 1, in 1.000. to lin 1,500,000 (or say 1 ; nch error in twenty miles) can he obtained. I have averaged the results of probable error in five separate bases measured, by the U.S. coast and geodetical survey in 1885, with a steel band of 300 feet, and it amounts te l_ in 840,000, or about l-13th inch per mile. Such exactitude is only possible with a measure of absolute length, the modulus of elasticity and co-efficient of expansion of which have been ascertained, and with tho work carried on under the best atmospheric conditions. The two base lines of the Spitzbergen arc were measured by a method introduced by Professor E. Jaderin, of Stockholm, in 1885, it differs, however, hut little from that employed by the U.S. geodetioal survey, except in respect of the length of band or wires used (Jaderin, 25 metres; U.S. coast and geodetical survey, 300 feet); and both processes give almost identical results, or about 1 in 1.000. or a probable error of, say, 1 inch in sixteen miles. This accuracy constitutes a forcible protest against qur present Chain standard differences, with their mean probable error of 15-lOOths inch per chain, or 12 inches per mile. The modern bases used for primary triangulation average about six miles, and do not exceed 400 miles apart • for secondary, three miles base, 100 miles apart; and for tertiary (commonly called minor trinngulation), lj mile base, and thirty miles apart. The cost of measuring these bases varies from probably not less than £4OO per mile for l-20th inch per mile error, to £3O per mile for linoh per mile probable error.

“These detail matters (however interesting) arc perhaps out of place when dealing with the mam question; so also the magnetic observations now undertaken by the New Zealand Survey Department ; and in the same category come tidal measurements, which are necessary to geodetic accuracy, and here as yet are inadequate. Wellington, Westport and Greymouth represent the South at present; while it requires tidegauges at the Bluff and Akaroa. to complete the surround and establish the necessary reference to ‘mean sea level’ for the South Island; and the North Island would require similar attention. “ The time has now arrived -when the perfecting of our survey system- has become necessary; and as we can largely advance the interests of science while doing so, wo should endeavour to compass the two aims in one operation. Looking to what has been effected, to what is now being undertaken, and to what is in contemplation, it seems scarcely open to question that long before the middle of this century is reached, all the pathways iu the Southern Hemisphere available to geodesy will have been trodden, that the New Zealand arc will, probably by then, have been merged in a great Australasian arc, extending from Cape York (lldeg. S.) to Stewart Island (47deg. S.), and that the Commonwealth will also have contributed an arc of parallel from Perth to Sydney. The question now is, if New Zealand,_ which takes ‘honours’ in most subjects, is prepared to seize the opportunity, and step into the front rank of science.” In an addendum, written after the perusal of papers and reports of date 1875 or earlier, Mr Eichardson says: “Mr J. T. Thomson, of Otago, estimated the cost of a complete scheme of survey at £303,000; but he spoke of the work lasting 75 years, of the use of a 36 inch theodolite, requiring 27 men for transport, aad oti*r eagsansire metkotU, all

lof which have been rendered obsolete by the use of modern appliances. In 1875 Major Palmer (then late of the Ordnance Survey of Great Britain, who came to the colony in charge of tho Transit of Venus Expedition) estimated the cost at £IOO,000. With the scientific advances made in the last quarter of a century in the instruments required —our greatly improved means of access —our topography practically complete, and our principal points mapped, it is obvious that even the latter estimate of cost would now he deemed excessive, and also that the cost of a precise survey for New Zealand canmot be appreciable!}' reduced by any further'delay. In 1875, tho date of Alajor Palmer’s report, our uncontrolled triangulations were only in progress. They have since been carried all over the colony, thereby widely extending tho area of our unascertained errors, and consequently intensifying the value of Alajor Palmer’s advice and warnings.”