MAGNETIC SURVEY.

New Zealand Times, Volume LXXI, Issue 4314, 25 March 1901, Page 2

MAGNETIC SURVEY.

AJST IMPORTANT UNDERTAKING. PROGRESS OF THE WORK. Mr C. Coleridge Farr, B.Sc., M1.0.E., who is engaged as observer on the magnetic survey of New Zealand, is at present in Wellington,_ after _ having made a series of observations in the north-. , When the report by Mr Farr publisaed in the 1899-1900 report of the Department of Lands and Survey was Written, observational work had been done at stations distributed along the coasts of the. South at approximately equal distances, with one at Half-moon Bay, Stewart Island, and four on the shores of Port - Nicholson. Beyoud the stations last-mentioned the survey had not been extended' to tbe North Island. In his North Island work, done since the report referred to was written, Mr Farr journeyed along the coast from W cllington to New Plymouth, thence to Mokau, and so on to Auckland. From Auckland he went along the East Coast to Cape Maria Van Dioman, and he returned to the Northern city by the West Coast. Observations were then made along the East Coast from. Auckland to Opotiki. The coast from Opotild to Wellington is the only part of the coast of the North Island on which observations have not, yet been made. A good deal of unfavourable weather was experienced in the north. All means of travel were used at one time or another, and, as may easily be imagined, the party had some varied experiences. In order to give an idea of what the survey means, the following extract from the 1899-1900 report may be given : " The instruments used have been those lent by the Kew Observatory Coinmitteo of (he Royal Society of London,'originally to Mr P., Baraccln, P.R.A.S., Government Astronomer, for the colony of Victoria, and now ’to the New Zealand Government. They consist of a Kew' magnetometer by Jones, marked ‘N.A.B.C./ and a Barrow dip circle, No. 30, and are provided with certificates of comparison, with the standard instruments at the Kew Observatory. . . . At each of the stations complete determinations of the depjination (known also as the variation), the horizontal intensity of the earth’s magr netic field, and the dip, have been made. These : three quantities are necessary and sufficient- for full knowledge of the magnetic conditions of any spot at the time of observation. For the determination of the declination tbe direction of true’ north has invariably been obtained from solar observations on the spot, for which the Kew typo of ‘instrument has been designed. The values obtained have from time to time, as opportunity offered, been compared with the trigonometrical bearings of the tnaiigiilation of tlie colony with concordant results,’ and as a very geiieral rule, with few exceptions,,the north point has been determined by both morning afternoon observation. The direction of magnetic) north has been derived from a magnet marked ‘V.’," which is part of the Kew equipment.. This magnet can be read to ten seconds of arc. riie horizontal intensity lias been derived from the usual method of vibration and deflection. Two determinations of ■ tho period of vibration of.tlie magnet V at the - same place., and time rarely differ by more than 0.0003 of ai second. This quantity (generally loioivni as H), freed from the effects of disturbances,is much needed for a recalculation of the Gaussian constants, from which the equal variation charts are constructed.. For -the dip, the usual method which eliminates all systematic error lias been used. - It involves the employment; ■of two needles,' and requires 144 vernier readings.” So far as observations have yet been made they have been confined to. Abe coastal .region, and no attempt what-ever-has been made to elucidate _ the Characteristics of the abnormalities which have been discovered. No observations have been made with this object iri, view.. What has been learned with regard to them has been tho re*suit of an attempt to form a skeleton picture of the isomagnetio lines, traversing the islands, for which purpose ..the stations have been spaced at approximately equal distances from each other. ‘ln the. systematic investigation of disturbances the will be placed ' wherV.bfigy arel’jnbj'h 'inquired. The' observations taken by Sir Farr oh' the coast’north of Wellington have . yet 'tdf ba reduced. ’There seems to be a' disturbance in the Coromandel district, ’ but, there are not yet sufficient grounds for a definite statement on tho matter.",’ThT other parts' of the North Island the quantities are apparently pretty uniform. ... Of. several disturbances revealed in the South Island, those in the Bluff and Nelson districts appear to he most pronounced. ' Others exist in the Otago Peninsula and in Banks Peninsula; indeed, the region between these two volcanic harbours is magnetically irregular. A possible explanation of this, says Mr Farr, would -be the existence of volcanic rooks at ho 1 very great depth below the surface of the Canterbury Plains. There is also a disturbance between Okarito and Gillespie!s Beach; on„./tlie West Coast; ” ’ ■ - ! One part' of the' work, which remains to be .carried but fe'the taking of observations at inland stations. This is necessary; in order' to fill in .what is lacking. Observations ’already taken have shown that Christchurch is a suitable site for permanent instruments. When these are installed they will constitute the fourth and most southern magnetic phseryatory, south of the Equator, the others being’ at ; Batavia, Mauritius and tablish, the permanent observatory in Canterbury, .and the necessary plans are being prepared by the Public Works Department. It is a matter of considerable, importance that the .observatory should be in‘full ivdrking’ qrdet. by.the time tbe British Antarctic expedition starts in August of this year. The taking of magnetic observations is to-be one of the important purposes of that expedition. , '.Sdmo of ’tho results of -the New Zealand magnetic survey, of interest to the nautical part - of the public, have been published in; the “ New ' Zealand 1 Gazette.'” Results for ecienfcifio purposes will not be published until the observer has imore,'leisure,,?and thepermanent ■observatory- 1 is in full working order. It is of interest to note that Professor" McAfQajr'(Tisi£mdia) and Professor Hogg (Melbourne) are now filling in the magnetic survey of Tasmania. _ A magnetic survey of Queensland, it is understood, is about to be undertaken.- . •