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APPENDIX VII.

THE MAGNETIC OBSERVATORY AND THE MAGNETIC SURVEY. Mr. Henry F. Skey, B.Sc, Magnetic Observer, reports as follows upon the work of the Observatory during the year 1904-5 : — During the past year the work of the Magnetic Observatory has proceeded upon the same lines as in previous years, and its operations have not been interrupted. For the major portion of the year the Observatory has had the services of two temporary assistants, Mr. B. V. Pemberton and Mr. E. Kidson, B.Sc, who were engaged to assist in the reduction of records as required for the use of the British National Antarctic Expedition, and the other similar expeditions. The Magnbtographs. The magnetographs have been kept continuously in operation throughout the year, and all records obtained have been carefully developed, &c, thoroughly washed to insure permanence, and after natural drying have been annotated and stored for measurement in their due course. The instruments are in a thorough condition of efficiency. No readjustments have been necessary except to the horizontal-force instrument, and this is always required in this instrument at intervals of a few years owing to the natural weakening of the suspended magnet witli age. This weakening may naturally be expected to be most rapid in the first few years of its life, and in the ordinary course of events will not necessitate a further readjustment before about another four years. The vertical-force balance has not yet required readjustment from this cause. The constants or the values of the sensitivenesses of the horizontal-force and vertical-force magnetographs were redetermiiied early in 1905, and the values found are given below, compared with previous determinations. The sensitiveness of both instruments has decreased slightly during the year. Adie Magnetographs, Christchurclt. (Equivalent of 1 millimetre of ordinate of the magnetograms). H. F. V. F. Date. Magnetograph. Magnetograph. C.g.s. C.g.s. units. November, 1901 ... ... ... ... 00000454 00000230 March, 1902 ... ... ... ... 00000457 0-0000269 May, 1903 ... ... ... ... 0-0000453 0-0000318 March, 1904 ... ... ... ... 00000460 00000312 April, 1905 ... ... ... ... 00000471 0-0000350 On the 30th August the temperature coefficients of the magnetographs were experimentally determined by gradually raising the temperature of the cellar in which they are housed. Simultaneous absolute observations were made in the Absolute House during the experiment, and these showed that the vertical and the horizontal components remained unchanged during the experiment. From the curves obtained the temperature corrections of the H.F. and V.F. magnetographs were calculated as follows: — H.F. magnetograph -f- l°Fahr. requires correction of + 0000015 c.g.s. units. V.F. magnetograph + 1° Fahr. requires correction of — 0-000015 c.g.s. units. These values, though probably somewhat smaller than the real values, have been used in reducing the term day records. Since the temperature of the magnetograph-cellar seldom varies more than a few degrees in a month, it is not necessary to have - the temperature coefficients verj' accurately. The V.F. balance appears to be overcompensated. The declination magnetograph exhibited no temperature-effect. Two iron pipes have been placed in the North Hagley Park to serve as referririg-marks in making the observations of magnetic declination. One of these is placed on the embankment on the south side of Victoria Lake, and its true local bearing from a copper tack in a wooden peg (HI.) placed in the Observatory grounds is N. 15 deg. 15 mm. 17 sec. E. The other, a larger one, is situated about 5 chains beyond the north side of the lake towards Trig. H. Its true local bearing from the centre of Magnetometer No. 1, placed centrally on the eastern pillar of the Absolute House, is N. 16 deg. 8 mm. 56 sec. E. These bearings were found from the survey bearing between H and " Sugar Loaf," and corrected for convergence of meridians between Mount Pleasant and the Observatory. The latter bearing agrees to 12 sec. with that found astronomically. Below is given a table of the absolute magnetic observations made during the year 1904, for the purpose of standardising the variometers. In the next table are details of the values of the base lines of the magnetograms thence deduced. The dates and times are New Zealand Civil time,

14—C. 1 App.