Eichardson. — On the Survey System. 493 



view, the merits and defects of our New Zealand surveys as 

 now practically applied. 



Among the noticeable defects I give first place to the want 

 of an absolute unit of measure for the colony. The second 

 defect, and a more serious source of confusion, is the want of 

 any provision to ascertain and eliminate the aggregation of 

 errors, which, though not excessive within any given square 

 mile, may become markedly so by accumulation. To these 

 and other points I now ask attention. 



The survey system first applied by Mr. J. T. Thomson 

 to Otago, and afterwards to the colony — a system of occu- 

 pation survey under check by triangulation — was mathe- 

 matically sound, and, even under the conditions of its 

 application, has resulted in our country occupations being 

 determined with probably as high a degree of accuracy as 

 obtains in any other country, and with a much higher 

 accuracy than has been attempted in most. Theoi-etically, 

 a primary triangulation with sides ranging from twenty to 

 fifty miles, and, say, a limit of error not exceeding lin. per 

 mile, should have been carried over the colony ; and this 

 should have been broken down to a secondary triangulation 

 with sides of, say, eight to twelve miles, the points of this 

 breakdown governing the working or minor triangulation, 

 which, with sides from two to four miles, would in turn have 

 limited and checked the errors of the occupation surveys. 



In the early days of the native troubles, and when the sea- 

 beaches and river-beds were the only available roads, the diffi- 

 culties in the way of a scientific primary survey were almost 

 prohibitive, and, apart from that, would have required much 

 time to effect, while the demands for occupation surveys were 

 of pressing urgency. To meet the circumstances Mr. Thom- 

 son devised a plan of local meridian circuits, with a probable 

 error not exceeding 2 links a mile, and with a locally measured 

 base (being, in fact, a minor triangulation without check), 

 but which would, however, serve for the time to fairly control 

 the occupation surveys, it being an essential part of his 

 scheme that subsequently the rigid primary work should be 

 undertaken, by means of which these meridian circuits would 

 then be brought into harmony and exactitude. 



We closed page "one" in 1895-96, when the Surveyor- 

 General reported (page xi.), " We have now a chain of tri- 

 angles from the North Cape to Stewart Island," and page 

 " two" still remains unopened. It will be easily understood 

 that in the sixties, when Gunter's chain was used, and when 

 the limit of error of chainage allowed was 4 to 10 links per 

 mile according to the character of the country, a triangula- 

 tion with a supposed limit of 2 links was a sufficient check. 



In the last March number of the New Zealand Surveyor, 



