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APPENDICES.

APPENDIX No. 1. REPORT ON THE SURVEY OBSERVATORY, MOUNT COOK, WELLINGTON. Mr. Adams to the Sukveyob-Geneeal. Sib,—- Wellington, 31st July, 1883. I have the honour to report as follows on the Survey Observatory, Mount Cook, Wellington, since it was placed in my charge in October last :— The Observatory building and the piers for the support of the instruments were not finished till early in November, 1882. As there was barely a month to prepare in, before the transit of Venus on the 7th December, all my time was fully occupied in taking observations for time and azimuth, and exchanging time-signals with the various parties who observed the transit of Venus. As I have already sent you a report on the observation of the transit of Venus, 1882, I will not refer to it further in the present report. The equipment of the Observatory at present consists of an eight-day astronomical clock, by Dent, of London, No. 38415; a transit instrument and zenith telescope, both by Troughton and Simms ; also a chronograph for electrically recording the observations, designed by E. L. J. Ellery, Government Astronomer of Victoria, and made by Joseph Brothers, Melbourne. The sidereal clock is suspended from a well-braced framework of wood supported on a brick pier. The compensation of the pendulum is effected by a cylindrical combination of zinc and steel. The rate of the clock has been very steady since it was erected in November last. The telescope of the transit instrument has an aperture of 3 inches with a focal length of 3 feet. The length of the axis from shoulder to shoulder (that is exclusive of pivots) is 18 inches. The pivots are 1J inches long and l-J inches in diameter. The transit instrument is provided with a very beautiful reversing apparatus, by which the telescope can be reversed in a few seconds, without any of the risk of disturbing the instrument that always attends the operation of reversing by hand. There are two finding circles, 4 inches in diameter, one on each side of the telescope. They are graduated to minutes, and can be set to show either altitudes or zenith distances. There are nine fixed vertical wires and one movable micrometer wire; seven of the fixed vertical wires are at intervals of about &s■' apart; besides which there is one extra wire on each side of the middle wire, and distant about 2' from it. There are also two parallel horizontal wires, about 3f apart. The integer revolutions of the micrometer were read from a comb in the field of view, and the micrometer head was divided into a hundred parts, of which tenths may be estimated. The first business of an observer is to adjust the transit instrument, to find the equatorial intervals of the wires, the value of one revolution of the micrometer-screw, the value of one division of the level, &c. The transit instrument was adjusted for collimation on the 19th November, 1882, and the adjusting screws have not been touched since. As neither the equatorial intervals nor value of micrometer screw had been determined at the time of the transit of Venus, the collimation error could not be obtained and applied in a direct manner; but its effect was eliminated by taking half the observations clamp east and half clamp west, and from these observations the collimation error for every night can be calculated by the method of "least squares," if it is considered desirable. The equatorial intervals of the wires have since been obtained from 60 transits of clock stars recorded by chronograph, and 30 transits of circumpolar stars recorded chiefly by " eye and ear." To determine these intervals in a satisfactory manner requires a large number of observations, and I shall therefore avail myself of every favourable transit of circumpolar stars that I shall hereafter observe in order to get a reliable value of the intervals. The mean value, as determined from the ninety transits already calculated, are as follows : There are nine wires, numbered Ito 9, the wire No. 1 being nearest to the clamp. For Clamp W. 1 =+41-7635.; 2 =+27-8775.; 3=+l4-0125.; 4=+9-2195.; s=--0345.; 6=-9-294;;.; 7= — 14-0265.; B=— 27-8465.; 9=— 41-6505. I may remark that Colonel Tupman employed over five hundred transits in order to determine the true value of the equatorial intervals. His transit had only five wires, so of course one with nine wires requires a great deal more calculation. The value of one revolution of the micrometer screw has been determined from four sets of observations on a- Octantis (s.p.), comprising one hundred and fifty-four observations in all, giving eighty-eight results. The mean value of these eighty-eight results gives 57"'943 as the value of one revolution. I should prefer to supplement these observations by others on different circumpolar stars, as it is only by taking the mean of a great number of observations that a thoroughly reliable value can be obtained. The value of one division of the striding level was not furnished by the makers, and, as there was no level-trier available, I affixed the level to a Troughton and Simms's levelling instrument, and, altering the inclination of the level, I observed the divisions on a levelling staff, set up a short distance away. I took two hundred and twenty-two observations, about one-half at a temperature of 62° and the rest at a temperature of 78°. The results, while showing that the average value was about 1", unmistakably proved that the curve of the bubble-tube was not regular, as the value of one division varied from ■§'.' at one part of the tube to 1£" at another.

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